There is no law where a admin can be held liable for removing member from group. But you can take the legal action against the admin if he is spreading or making and publishing defamatory remarks against you. It is an penal offense. You must lodge an FIR with local police u/s 500 r/w 34 also for criminal intimidation and offenses under cyber law.
The first step in starting your defamation case is to figure out whether or not you actually have a valid claim. Perhaps the best way to get a rough answer to this question is to look at the elements that come together to define defamation.
Though states may vary slightly as to the specifics, in general all of the following elements must exist in order to establish the speaker’s (or publisher’s/poster’s) liability:
1. publication to someone other than the person making the claim (a third party must have heard it or read it)
2. the statement must be false (if what was said/posted/published was true, no matter how embarrassing or harmful, there can be no defamation case)
3. the statement must be offered as a fact (rather than as an opinion)
4. the statement must injure the reputation of the person being defamed (the “plaintiff”), and
5. the statement must not be subject to any kind of privilege that might shield the speaker/poster/publisher from liability.
Reference: Section 500 of Indian Penal Code 1860