Refusal to cancel expired contract.

Just received a call today from Mondo consultant to offer me “a great deal” after my Telkom rooter and cellphone contracts expired. After I accepted the “upgrade” to 20G on the rooter I asked the consultant to please cancel the contract on the sim or convert it to pay as you go. He was not interested and told me to call the call centre. Now I’m sitting with additional costs for the upgrade which I did not even need because he couldn’t cancel the sim contract so I can afford the “ upgrade “. How does Mondo permit selective changes on contracts that have run their course and are now on month to month - allowing only changes that increase the costs? I’m now inclined to cancel the whole deal as there seems to be a lack of good faith in this upgrade offers.