BAD BAD BAD SERVUCE

I got my phone back from Cell C after to weeks. I spent over r 800 on a secondhand phone and a new sd card because Cell C did not come to the party and arrange a loan phone as prommised. The phone is now worse of thatn when I sent it in. It does not even read my sd card and still has the same problem of not conecting to the computer when using the usb cable. That is why i bought a new sd card. I put my sd card in my husbands phone last night and it works so it is clearly the phone that is the problem. Please can you assist me in getting Cell C to give me a new phone as this phone was a faulty phone from the start. The technician of Nokia on Cape road told my husband himself that my phone was faulty to star off with. Cell C get their money every month but I just have to take their bad service. My phone has been in 5 times in 4 months.