I think it's their only way to "escape".
Telegram can generate new links through api, I believe they simply do so.

The only limitation they have is that, by changing the link, they lose the functionality of the old link.
I think that sooner or later they will get tired. The antidote is to be fast, the faster you are the easier they will get tired.

I don't know your every step from moderation, so I can't give advice on how to speed up removal. I think that you are doing a great job about it anyway