Denying a refund using bad address

I have an odd situation. I had a very short lease on an apartment and left it clean and in the repair in which I received it. I also gave 60 days notice of move out and a forwarding address, which they required as well as the notice. The landlord says my entire deposit is due back and claims to have mailed it out. When the refund failed to arrive about 2 weeks later I called to confirm the mailing address and that the deposit went out. I was told the date they have is a check printing date, not necessarily a mailing date. Well, even mailed the next business day the check is overdue. Mailed any later and it is too late to be within the legal period for return. No matter, no one can give the date the check was actually mailed. I asked for the address to confirm they had not mistyped. They then said the refunds are mailed to the address I have vacated more than 30 days ago. It is up to the post office to forward it to me. I have a PO Box, and never received mail at this address, so never put in a forwarding order with the post office. It seems the policy of sending the refund to an address they KNOW it needs to be forwarded or will get returned to sender is deliberately designed to delay or deny the rightful refund. The management company refuses to even consider this a problem until an additional 30 days has passed. What remedy do I have to get my deposit actually in my hands in a timely manner? What possibility do I have for filing some sort of grievance about this practice of failing to use the correctly provided forwarding address?