Raw deal from Cell C after 12 years

I have been with Cell C for 12 years but this year they showed me flames, I transferred money to them by accident and they also debited my account as per agreement as I have a contract with them, I called to rectify my mistake and I was told that they thought I payed in advance, I got a call from the supervisor and she told me that they thought I was paying a debt that I owed them, so all in all I will not be getting my money back. Apparently I'm in arrears that were not communicated to me. That's not all I actually wanted to upgrade in this year and I was informed that I can't due to affordability and this is 12 years later when my account has been payed every year, every month on time, I was called by a manager from head office who was supposed to call in October to date I'm still waiting for his call. I want my upgrade as per the sms's that I receive and I would like my money back that I had payed accidentally to them,it was not an arrangement that I agreed to.