Why would Sprint not unlock my iphone 4s even though the usage was way beyond "90 days"- Jan 2012 to Oct 2012, and I am living outside of America?

I went into contract with Sprint in Jan 2012, and had to terminate my contract with them as I was moving out of the United States. When I spoke to customer service, they asked me "the reason for my termination" and I specifically told them that i was moving out of the country. They basically asked me turn in the phone to Sprint or pay $300 early termination fee. I paid them $300 so i could keep the phone. BUT, not even my international SIM card works on the phone because Sprint won't take the carrier lock off. Instead in Nov 2012 they sent me some random tax bill of $35, which the customer service hadn't bothered to tell me about.

When I went on their support site again, this is the what I found: https://community.sprint.com/baw/message/705416

I reached out to the again today and i am waiting for their response, but their customer service agents are SNOBS and probably going to respond with "we can't" and "we won't".

Now, I have an iphone 4s that is fully paid for, I don't live in America, and yet i can't use. It's nothing more than an expensive paper weight.

What should I do?