No, I cannot ban their ISP because they use VPNs. They bounce all over the world and there is no effective way to trace them back to the origination IP without hundreds of hours of work. Think about those ransomware attacks that you hear on the news. Even the FBI and CIA have a hard time finding out where those crooks are originating from. And they don't even have to trace backwards. The crooks are demanding Bitcoins. They could trace forward to see where the Bitcoins end up. They say Bitcoins are anonymous. Even though it is anonymous, it is still traceable. The public Bitcoin ledger allows anyone to see where that Bitcoin was received and where it was spent or transferred again. You follow that path, and work back from that, you'll eventually find the person who received that Bitcoin. Obviously I don't have the resources of the FBI or CIA.
Sometimes people go out on Saturday nights. The first spam message was posted about 7 hours ago. You don't see the ones I delete on a daily basis because, well, they're already deleted and gone. They do come on a daily basis, and often multiple times a day. They do seem to follow specific time patterns. Usually at 4am, 8am, and 3pm. Today's spam came at a time that didn't follow their usual pattern. Perhaps they got wise to when I look out for them.
I delete spam messages and I ban accounts if they are proven spammers. For the legitimate users, I only delete messages if someone clicked that "report" button. More often than not, those reports have no merit and I ignore it. If you think that your messages don't offend anyone, think again. Someone clicked that report button.
Out of thousands of users I've only banned 2 legitimate users. Those were temporary bans and they can come back if they wish. That's up to them.