Call Centre

I have a contract with 8ta, this is the second contract i have with them, my contract is fixed for r140 per month where i get 100 free minutes and 1GB data, if i want any additional airtime i must call in to buy it. In the beginning when Telkom phoned me to ask if i want to renew my contract , i agreed and asked them not to put any additional spending limit on it. it was always working fine, 3weeks ago, my minutes was finished but i was still able to make calls. I Called in to the call centre after explaining to the agent what was happening se assured me it was free airtime and that i wont have to pay for it. i recently got my billing statement and it shows i have to pay for that airtime. i wrote down the time, date and the name of the agent. i want you to go and listen to that conversation. i refuse to pay. I called in again to log a complaint but no one has got back to me yet.