I have gotten down vote on almost all of my questions at once!
How should I inform the moderators to check this sabotage and give me the lost reputation points back?
Moderators cannot actually manually invalidate votes (well, except if it's obvious sockpuppetry for reputation gain; then we can just delete the account and remove all of its votes). If you would like a moderator to check your profile for suspicious voting from other users, you can flag one of your own posts for moderator attention and explain the situation to them.
Usually, the system will detect these votes automatically. If too many votes are cast by one user towards another, whether upvotes or downvotes, the system will detect that and invalidate the votes, simply removing them directly. This will show up on both accounts' records and does not carry any consequence but may be used by a moderator when investigating or deciding how to take action.
Overall, I wouldn't worry about it too much. The script is likely to revert it automatically anyway, and it's easier to gain more reputation back by participating than spending that time trying to revert those downvotes. It's frustrating, but the system has built-in protection against most vote fraud and upvotes grant five times more than downvotes take away anyway.
Please take everything given below as guidelines (not set in stone). Some may differ from these and that is okay. It is not a challenge to them as these are only my opinions based on my participation in Stack Exchange for 8 years and what worked for me what didn't. I've committed every sin (except head games) shown below however I have always learned from my errors or at least tried to.
I wish to give you some constructive criticism that I hope you will take by heart but first I want to make something clear. I have a passion for helping others if I can, not push them down at every opportunity. That member voting you down is NOT me. I only upvote posts I find useful. If I don't like a post I do nothing and move on to the next one. I don't even know what badges or privileges I have and I don't care. However because your post drew my attention I upvoted it even if it didn't deserve it (this will be explained shortly) and upvoted hyper-neutrino's reply which was very deserving. I cannot improve on his answer so I will give you one from a different angle.
I think I know what is going on and it's all psychological. In high quality forums (they call them communities now) like Stack Exchange (probably the world's best) and other social networking mediums which reward it's best users with additional reputation points, badges, features, privileges, etc. I've observed that some users develop a smug i'm-better-than-you attitude. If your posts are anywhere near that gray area of minimum requirements some users with higher reputation or who recently earned a privilege will begin judging others' work a bit more harshly. However that is not always the case.
Based on a very small sampling of your posts in Mathematica (about 5) I observed that most feel like they were lazily constructed only writing one thing you tried and usually it's only one very short instance of code with almost no context. You don't even mention that you studied the official documentation but something about it was confusing and you want clarification. It's only as if your posts say I only tried this, please fix it for me. Those are all beginner mistakes (on forum etiquette) and it appears you're still making them about a year after starting as a member.
Even this question in Meta is only two sentences long. You didn't even provide any links to questionable posts that were downvoted so that other members could examine them for you and give you feedback of likely reasons they were downvoted. You even decide on your own that those downvotes were sabotage instead of asking if they were justified and how they can be improved.
Better posts show more examples of code (usually simpler code that works or halfway works using other algorithms or native functions) that somewhat succeeded and samples that didn't work and the results given. Good posts also explain why they believe it didn't work by stating what they do understand and what they don't.
One way to demonstrate this is by revealing your programming experience or math level (i.e. I'm 1-year novice in Mathematica with mathematics up to systems of partial differential equations) because sometimes errors occur when attempting to solve an application with math that is above one's level (I've done this many times). However keep this very brief to stay on topic. Some communities like Stack Overflow are very touchy about this.
Better is to demonstrate which niches you are most familiar with. For example I can solve the following multi-level transformation with
MapThread (showing one or two examples) but my attempts at solving this with
ReplaceAll (showing at least two different attempts) fails or only partially works.
When you do this it is a huge win-win for you and readers of your posts. You will learn how to find answers on your own so that the fewer posts that you might still need will be much more interesting. This also helps members better explain things to you in language you will understand and where to find the right resources in the documentation.
In short your posts need to show what you've researched and attempted to arrive at the answer on your own. Stack Exchange should be the last resources you try when all else fails not the first thing you draw upon. This way you can ask deeper questions which demonstrate that you really care about learning the material not just have someone fix it for you.
I invite you to examine any posts I've done for samples of going too far which I sometimes do. Also notice that I respond to all answers and most comments and I never forget to upvote any of them if I learn something or if it appears they really put a lot of thought into their answers or comments even if not very useful. And finally, never forget to thank anyone who genuinely tried to help. It's called appreciation.
Although sometimes less is more that is not the case I've observed with your posts. I hope I wasn't too harsh and you really learn from this.
I'll keep adding more over time.