I agree I'm in the same situation as you,these days people with channels just join ICOs channel and start adding members to their own channel and nothing can stop them.I'm pretty sure that OP service is based on doing that.I think Telegram has to implement a new feature that will banish this kind of behavior.Maybe asking the user some thing like:"XX user has invited you to this group,Do you really want to join?" And if the user doesn't give an answer,the invitation gets automatically deleted.