getting declined for an upgrade

I've been with cell c for the past 8 years if not 9 now I keep getting sms's that I owe cell c but when I call the customer care dept they tell me I don't owe anything and according to my knowledge as well all my accounts are up to date now I'm due for an upgrade I normally pay R839 every month I need to upgrade with a package for R699 but I got declined which I don't understand. Each and everyday I get emails if not sms's saying I have been handed over can someone call me and resolve this. my number is *** my main contract number is ***.