Same happened to me but with Orange. Razri stopped working twice, managed to get a replacement phone but that developed the same fault. At this point it was out of warranty but after many phone calls and emails they offered me a Moto G ( no Razri handsets available) or an upgrade with a new contract or buy out of my current contract.
I reluctantly took the Moto G with £5 a month knocked off my monthly bills.
It’s not a bad phone, it’s probably faster than the Razri but the screen and camera are not as good. Also mine doesn’t have a memory card slot so memory is a problem. It’s been more reliable though 🙂