Diversified Consultants Collections for Sprint After settling a debt for closing sprint account early paid over $900 and they said still owed $350 Internet

I settled a debt with NCO financial who collected for Sprint after cancelling my contract early.  The bill was removed from my credit report because I had checked due to the fact that we are trying to buy a house.  After getting the zero balance later, which was a settlement offer to settle in full.  I begin recieving nasty calls from this company saying I still owe Sprint $350.  I have faxed the zero balance letter to them and they still say the settlememt wasnt accepted and I need to pay $350 more dollars to Sprint.  I was charged 1300 dollars for a cell phone bill that I did not even cancel.  My boyfriend took the bill out of my name and put into his because he didnt have the money to pay the one month bill. this was all done without my knowledge.  I still have Sprint and I feel they have gotten enough of my money