Any clue what can be wrong with my phone?

ok, here is the deal, I got the tmobile comet phone in june 2011, & it has been a headache since I got it. A few months ago, I got a replacement phone because my original phone volume was going in and out. Now the issue I'm having with this new one is the phone wont keep a charge...i went and bought a new usb part and it still wont keep a charge. I have noticed when I charge it on the computer it charges but this wall charger isnt charging. Tmobile wont send a different phone period...they just keep sending the front part of the phone....now they r suggesting a battery but I'm so over this phone. Any clues????