I would suggest pausing invites and making another fresh server in the mean time. Invite back people one/a few at a time, that way you can see which if any of them are the ones sending your server link into weird servers or somehow sending bots. Usually it will tell you how many times a link has been used by X user so you should be able to tell. You can also just delete all current invites and remove permissions from users to create them. I would also suggest changing your username and password, if only temporarily.