Cell c upgrade

I recently upgraded my sim package with cell c and they took all my data for previous contract and some consultant named Neo rudely told me that the rule say I forfeit my data for old contract. How is that possible when I am paying for full package for the old contract, why are they taking all my data and give me small data yet I'll pay for both? Ive been using cell c for years and this has never happened. I upgraded 2 years ago and my data was there, I had no problems. I'm so dissappointed I don't think I'll carry on with cell c if they treat me like this