Cancel tmobile contract?

Ook out a tmobile 18 month contract 10 days ago. The phone is faulty! Went back to the shop, they said they would not give me a new phone because it's been over 7 days, but they would send it off for 2 weeks to be repaired (I've only had this �500 phone for afew days and they want to send it off for 2 weeks!!!) I said this was not acceptable! Rang tmobile customer service when I got home, the person I spoke to said he would send a replacement out the next day between 8am-6pm. Took the day off work, at half 6 I rang customer service who told me the person I spoke to should never have said I could have a new one, because I bought it in store I only had 7 days for it to break to get a new one! That a manager would ring me back and that the only thing I could do was have it sent off for 2 weeks for repair (seriously!!!! On a bran new phone???) I'm not happy at all! When I asked about canceling the contract (after just 9 days) and offering to pay for the full first month, I was told I'd have to pay the full 18 month contract!!!! Surely there must be a way around this! I've had the phone less than a fortnight!!!! Can I angel and give them the phone back without having to pay the full contract???? What will they do if I just cancel the direct debit and give them the phone back??????? Any help or advice would be much appreciated! Thanks