You can find the PA laws to quote here:
Security Deposit Law Guide 50 States | Landlord.com
I agree with the above - you gave proper notice. The keys don't matter.
He probably berated you for moving out because he doesn't have your security deposit anymore lol!
Anyway, send a demand letter with a deadline to return the deposit, then sue in small claims court if he doesn't comply.
Here's a sample letter:
Dear LL:
Please send my security deposit refund in the amount of $_____________ to the address below by ______________(give him say 10 days).
As you have not complied with Pennsylvania landlord-tenant laws regarding the return of security deposits, per 68 Pa. Cons. Stats. Chapter 8, Sec. 250.511a, you have forfeited any rights to the deposit and must return it to me in full.
If I have not received my full deposit refund by _______________ (date above), I intend to pursue the matter in small claims court, and will ask the court to have you reimburse my court costs, as well as any punitive damages allowed.
Hopefully, this is a simple oversight, and I will receive my deposit refund shortly.
Sincerely,
You
Your Address
If he calls you and tries to say you didn't send the keys back on time or something, just say that's a non-issue, as he did not comply with the law. Just repeat this as if it's a mantra.
It was a non-issue anyway, but the fact that he didn't comply with the deadline makes any claims against deposit moot, so don't waste time arguing them.
Good luck :-)