[Q] how can I unlock Xperia z1s c6916 T-Mobile? topic

hello there I hope I'm not posting this in the wrong place :)
So I bought this z1s on craigslist and it worked for a month but now it stopped getting service. I checked the IMEI and the phone now is blacklisted :(
so I thought I could just unlock it and use it with other carriers!
please if you know a way to make it work let me know