TMobile Transferred Service with a Zero Balance Tmobile sent me to collections! Internet

 I had Tmobile for years, when we moved from Portland to florida i kept service for a little while then transferred the service to a friend.... I got MetroPcs.... So a year passes and I am all set to buy a house. Go down to the bank and BAM there it is tmobile on my credit history for $2500! I immediately went to the tmobile store where I did the transfer. The same person who transferred the service said yes it was and gave me a printout. Transferred at a zero balance. Called Tmobile thinking this was some sort of mistake on their end since their own records showed it was transferred but the ****** on the line who dared call herself customer service said sorry there is nothing we can do it is in collections. So i got the number for collections and they said sorry we have to hear from tmobile to remove this. WHAT THE HECK. I have all the evidence yet I am getting a run around what is wrong with this? Do I have any remedy here? I have sent the papers to the credit agencies to have this removed is there anything else I can do?!