T-Mobile locked to a carrier this morning at 7

Hello! I recently got a iPhone 8 Plus 256 GB T-Mobile for Anthony so he was using it. Anthony locked T-Mobile SIM card. When I try to get back to SIM card, it keeps asking for your PUK code to unlock it. Sent a email stating I need to unlock Anthony’s iPhone 8 Plus 256 GB T-Mobile

they replied saying the PUK code is 0000

ok

what should you do?