Unlocking question

I recently bought an AT&T note 4 to use with my Simple Mobile (Tmobile) service. When I requested the unlock code from AT&T, it was denied because the previous owner still had payments to make on their service. So my question is will one of the paid unlocking services be able to provide the unlock code, and if so, is there a particular service that is recommended. A general search returns a vast number of different services with a broad range of fees.

Thanks in advance.