WAITING FOR MY PHONE SINCE JANUARY

I bought a phone (Samsung tablet) on contract from cell c 2015 November, only to find out that its microphone is not working. I returned the phone for repairs early in January 2016, they said it is going to take about 21 working days for them to fix it and return it to me. I didn't receive the phone after 21 days, then went to query about it. I was told the phone was still in repairs, up till today. My main problem is that, I have been receiving and paying a cellphone bill of a phone that has not been in my possession since the beginning of this year. I need your intervention please.