Billing dispute

I have a problem with Cell c,last year I took a contract phone( Nokia Lumia 630) for an amount of R170 every month,bt I am billed for two phones & they deduct R333.On the 10/03/2015 I lodge a query & I was told to email an affidavit, Id copy & a delivery note.I got a respond with a case nr:*** and reference nr *** that my case was reffered to ***** department and they will contact me within two days.I was promised that they will sort this matter but till to date no one called me back,I decided to change my acc until they sort this matter and now I am in arreas,so please help me because I can not pay for somethig I dont have.