The buyer did agree "to not call you anymore", so when he calls agin, keep reminding him of that.......
So, when he calls from now on (he will), kindly advise him there's a charge for tech support from now on, $10 per question, or $50 per 30min call, and must be cleared in paypal before you can answer his questions....he wont call back.

I could tell you some other ideas here, or i might just call you lol 

I've done similar to this before, it works quite well. Mention money and they crap themselves.