I've seen a few emails and texts individuals have recived after quiting their jobs. I would like to offer this up for everyone to evaluate as a possibility.
“I am no longer employed by you. If you continue to contact me, you are agreeing to pay my consulting fee. Any further comunications, or questions regarding this fee will be considered billable hours.”
Or something similar to this. The idea being, you keep wasting my time, I'm billing you for that time. If they contact you, then you write up an invoice for a few hundred dollars, and you send that invoice to proper channels. If you haven't heard back from, you send the invoice to their management. Maybe threaten to take them to small claims court over their lack of paying. I'm not 100% sure if that would work, but it might be fun to try.