Short-Term, just set up Gmail filters to catch emails with common keywords (“featurii.com” seems a dead giveaway and manually report these emails as spam to train Gmail’s AI.

Long-term, you need to go scorched earth. Review-bomb them on x, googlereviews, fb, alternativeto, etc. If you do it enough times you will get a VP's attention, and they will come to the negotiating table.

Also, worth a shot to report the issue to Google to investigate Gmail account misuse. Maybe even contact Customer Service directly if they have one, an underling may just want to care. Heck , most effective, have a lawyer friend lend you a company letterhead and have GPT send a fax/email to their registered agent or legal@ , with a cease and desist demanding they stop. Friends & vendors will put your script on letterhead free of charge.