Can anyone help me with a carrier lock?

Sep 24, 2018
A week ago my 16 year old son was held at gun point the guy wanting his wallet, my son didn't have his wallet on him so the guy took my son's phone. I have a extra phone that my son can use but it is carrier locked and T-Mobile says they can't unlock it. When I was using it I was going through My Family Mobile but they got bought out since then and the new owners are giving me the run around. Please, can someone help me out at unlocking this carrier lock so that I can give me son a phone to use. Thank you in advance,