Blacklist of users – blocking users

I can’t figure out the best way to create a blacklist/ban list for users. For example, currently on the site, when users add a post, they select a pricing plan with a limit on the number of posts they can publish (although I don’t need restrictions, but if I disable them, the copyright button doesn’t work). And now a spammer has registered who adds irrelevant posts. If I just delete him, he can register again.
I tried to go into this user’s pricing plan settings and change the limits—set everything to zero—but it didn’t work; the system says that the minimum must be 1.
I tried adding a new tariff plan with zero restrictions, but I don’t understand how to move the user there, I couldn’t find where to change the tariff plan for an individual user. And the question immediately arises: if I move him to the “Blacklist” tariff plan, he will still be able to choose another free tariff for publication when he tries to publish.
In general, I don’t understand the logic behind “banning” unscrupulous users.
Please share your thoughts.