Locked iPhone 5 on Sprint carrier

IDKIDK

Commendable
Feb 10, 2016
1
0
1,510
Hi, I have problem with my iPhone 5, I bought it from some guy on internet and I can't contact him anymore. This iPhone is locked on Sprint carrier but I want to use it with T-Mobile. I called to Sprint and chat with Sprint service but they always need my Sprint phone number or contract number but I have got no number. Please help.. what I have to do to unlock it?
Thank you