I recently bought a new S7 Edge on Ebay but it is locked to T-Mobile, My carrier is AT&T so I try to unlock it but it won't let me die to the obvious unlock eligibility for T-Mobile. So I buy an unlock code and follow the instructions to unlock it but then my phone starts that it is not registered to any network. I have no idea what to do since I can't even place an unlock code. Is my only choice to join T-Mobile?
Return the phone to the seller if they listed the phone as unlocked.
Tmobile will only unlock their phones for Tmobile customers.
There is a way to see if the phone is blacklisted. It is easy - but I forget how to do that.
Manage your T-Mobile account