Blackberry Problem

I renew my phone contract somewhere between March and April 2015.<br> I had the Blackberry 9720 for a week when it started giving me problems I took it back and it was changed without any problems.<br> Two weeks later I was back as it gave me more problems than the first phone I took the phone back and they said they cant change the phone or give me a different phone they must send it for repairs I asked them as that is my only phone to borrow me a phone they refused.<br> Please assist me to get a different phone as I cannot struggle with a phone that just switch of by itself and takes up to 2 hours to go on again that's after removing the battery and try whatever possible.<br> I don't want this s**** phone anymore please assist me as I need this phone in my daily work activities