USPS Lost phone, Xfinity should keep promises!

I sent my old phone to Xfinity the tracking shows the phone is still in Texas since april. USPS lost it twice they lost it in right away by not scanning it, then lost it in texas, apparently it just showed up at Xfinity but because I didn't send it in time they sent it back, I have no idea when its coming.....but they are charging me $700 for not sending it.....Xfinity your lucky I don't want to deal with new cell phone companies, I'll unfortunately be paying it....late after my phone was turned off but come on!!! Stop using USPS this clearly keeps happening!