Cell C the Worst Service Provider

I previously enquired at Campus Square Cell C branch if I could use airtime to purchase the 200GB annual data package and one of the consultants confirmed to me that I could. Over the last year or so I have been loading airtime on my phone so I can buy the data bundles. I have now been told that I cannot buy the bundle I want through airtime. I am not stuck with over R3000 worth of airtime. I feel so let down by Cell C. I find this highly disappointing and *********** of their staff.