Scammed by T-mobile, now what?

I also got scammed by Tmobile. A representative told me the there is a mega promotion and that I would able to be get 70% off a new phone. I agreed to the promotion after getting my phone I noticed that the only promotion I got was my trade in value. I called to get this resolved, the representative assured me that it's taken care of. I noticed again that I'm being charged full amount. I called again but this time they told me that there's no such thing as a mega promotion and that there's nothing they could do. I told them that I would like to return the phone and leave T-Mobile. They told me I can't do that. I also offered to pay full price for the phone just so I could leave but they said that I can't. This is a scam company you will have better luck buying a phone off Craigslist.