unless you have made a seperate deal with t-mobile extending you contract to get a loyalty deal (as in you dont get a phone you just get more value for your money) then you should be entitled to a upgrade either every 12, 18 or 24 months.
If you still cant get one phone t-mobile redemptions and ask for your pac code as (network) has offerer you with (phone) with x minutes and x texts for �x (make it realistic, I would check the deals on the market first as t-mobile redemptions will try to beats as you have been a loyal customer.
Alternatively, pop into a phone shop and see what trade in deals you can do, most shops like the carphone do trade up's of �200 that would be more than adequate to pay off your contract.