There is the fingerprinting option not sure if that would work for you:
If you’ve already banned their I.P. and e-mail vpn wouldn’t make any difference if they use the same e-mail, but guess they are using different e-mails and I.P.s then so ban isn’t working.
Don’t know what “4h1t” means, that is a strange post there Ammonia and Bleach are definitely not safe to be mixed that generates toxic gasses.
I would like to second this, it is free (using Gemini for example) and you could have custom instructions that block even if the troll becomes more sophisticated.
The trolls experience would be quite bad as well, cause they would get block right away and only you would see the spam in your queue which you can easily delete.