Phone at repairs for over 4 months

I took my phone for repairs in July, after 21 days when I was supposed to get my phone back I was told it was brought back unfixed. Apparently an SMS was sent but they knew I didn't have a phone. The phone was booked in again in August when I went to check my phone at Highveld mall the phone was still there unfixed and when I complained they said its not their fault. Now fast forward to November my phone is still not fixed and there's no communication, I call Telkom all the time and they keep on telling me they will investigate and come back to me of which they never do. I get billed R650 every month for a phone that I'm not using for over 4 months. I'm really getting a raw deal and am not treated well as their customer I mean 4 months without a phone but you are billed every month? What nonsense is that??