Incorrect information via call centre

I have purchased a data bundle that was offered to me by the call centre. According to the operator the 10G bundle does not expire. I asked her more than once is she sure on which she rep****, yes it does not expire. The bundle was supposed to be loaded to my secondary account, but as I thought it would happen, it was loaded to my incorrect cellphone contract. to my surprise, I have received another 10G, today, just a week later. My calls logged with MTN does not even get followed up by them. What should you do to get some feedback, and all they do is mess it up further and this will be billed. I will cancel my debit order as this is going to be a very high cellphone account due to incompetence.