Simply reported these guys and thats it. Cant stop creating multiple boards unless those users got reported and mods take a ban hammer on them termporary or depends on the gravity of spamming. Since its in the official rule can easily banned them. But its gonna be worthless since they can just create a new account after that.

Probably he will just create new one and do it again. So I think there should be an alternative solution to it that might help in decreasing spammers. (of course reporting but Im thinking an extensive one limiting those users or restricting their post allowed something like that, depends on rank or level of their posting and contribution).