billing screw ups

I refuse to sit in the phone another 30+ minutes to address the same issue I've already waited patently to address. I returned a modem, the second one in less than 1 year due to poor service and coverage in my city-center home. I am being killed for this piece of equipment.  During my last conversation with T-Mobile they located the equipment I returned and said I will not be billed for it yet it showed up on my bill. I appreciate the fact that I get to talk with people when I call and have chosen to remain a cost per in spite of poor service in the rural areas that surround my city. This level of incompetence will be what drives me to find another carrier. When I return a product, in the provided box, and that piece of equipment is located when on the phone with customer service and I'm still geing billed for it is stupid! Fix it or white me off as a customer! If I have typos it's because I don't have my glasses and I'm too pissed to wait until I do.