There is a process for removing moderators, but it seems unlikely to be relevant in this situation. Moderators are democratically elected* to handle exceptional situations. so they often come under extra scrutiny. But truthfully, regular users determine how each site operates.
One important principle of moderation on Stack Exchange sites is that we don't ask moderators to make decisions based on the correctness or accuracy of post or comments. Those things are better measured by voting. I'd be surprised if the moderator in question "doesn't know anything about the subject", but that wouldn't really harm their ability to moderate this site. The decisions moderators make normally revolve around content that is clearly out of the bounds of according to site norms or resolving conflicts between users. Knowledge of mathematics can be helpful, but it's not critical as a rule.
To make a guess about what brought this on, it looks like you've had some answers deleted. One of the principles of a Q&A site is that answers must directly address the questions asked. Your answers were deleted by a moderator as a result of 7 different flags by other users. It seems the consensus of the community is that that those answers don't answer the question itself.
My suggestion for the future would be to carefully read the questions you are interested in answering and post answers that address the precise query the asker posed.
* Except on beta sites where they are appointed by Stack Exchange Community Managers. Also, MathOverflow has a unique history that would have an effect on changes to moderation that I won't go into here.