Shadowban Bots by pattern
Should be simple: have something similar to automod check for known and reported bot messages and their pattern. If it matches, rather than blocking or reporting the account automatically, just cause the suspicious message to be hidden from anyone but the sender.
Additionally, after 1 month of their infraction, lock the suspect's account and try to make a direct contact with them.
Another thing to do would be to change Verified → Partner and create an actual Verified Account status that marks accounts that are confirmed to be actual users rather than bots.