maybe we can add to group, so every post will moderate but the problem is they will make another account
That wouldn't help much, as you already know new accounts would be created to continue with their nonsense, unfortunately, they don't realize how useless it is because their posts will be deleted. What is more effective is to lock the thread and give the OP a chance to reopen it after a simple PM, although it is something that never happens, since the OP doesn't care about the thread at all. In any case, if that user does the same thing again, they will have one last step to have their account blocked.
It wouldn't be bad to have a specific tag/badge for such accounts, that would probably end their shill journey on the forum.
As for the creation of new accounts and the movement from the beginning, they are quite easy to recognize, and it is honestly not a big job for me to expose them and present them here.