Phone that went to repairs a million times

I took a contract with cell c. A blackberry 9720 which only worked for 8 months properly, this phone went in for repairs 3 times and this will be the 4th time it goes in for repairs with the same issue. I have bought a number of batteries because I thought that the problem is with the battery which is obviously not. MY phone would go in for repairs and it will only work once and when is am supposed to charge it gives an error of a faulty battery. I am now getting fed up of this because every month I am paying for a phone that is not working and because of this I am thinking of not upgrading my cell phone with cell c when I am due for upgrade.