Can't load airtime on contract

I got a new contract with Telekom for the first time 2 weeks ago. My free minutes have just ran out so I tried to top up with prepaid airtime, I tried a few times and it didn't work. I phoned Telekom to ask why it's not working and they tell me that if you are on contract you can't top up airtime. The process of loading airtime now is a major issue for me. They did not inform me about this before I signed up for my contract