Upgraded to a top up contract - but now I can’t top up cause I took an iPhone

I upgraded my Telkom contract on the 18th of August in the iStore at Cresta. I double checked on atleast 3 occasions if it will still be an open contract where I can increase my limit and buy additional data bundles and the sales assistant assured me and said I must just phone Telkom whenever I need to increase my spending limit. A month in I tried to purchase a data bundle, but it kept failing. I then phoned the Telkom call centre who informed me it is because I have an iphone and you cannot purchase data bundles on more expensive handsets. They can collect my iphone, give me a cheaper handset and only then will I be able to buy data bundles. How on earth does this make sense??? I would never have taken out another Telkom contract for 3 years if I knew I wasn’t able to use it after using up my data. I am basically now paying for an expensive camera without being able to use the phone. The sales person **** to me to get me to take out the contract, the call centre person assured me someone would phone me back and a week later I still haven’t heard anything. I am furious! Please rectify this immediately. I am paying for the data so can’t see why I can’t use this. I use this phone for work, so I need to be able to buy data when needed.