How do you deactivate a phone?

A

AC Question

I have an htc desire 510 and I have called my phone carrier, where I bought the phone from and everything else and nothings working, so I tried to go to device administrators and that didn't work and then I tried to google android device manager and tried to do it that way and that didn't work so finally I called your company and the guy told me to do the same thing I had already done and said there was nothing else we could do... So am I supposed just pay two phone bills? Like what am I supposed to do!
Sincerely, Fed Up