Incorrect billing

I had a voice contract with Autopage since 1999, after contacting them to cancel the contract for R69.00 a month which i no longer use, Xavier advised they now have a special for R79.00 on their tablets which is a data contract. I decided to take them up on the offer and divert the voice contract to a data contract, as I do have wifi at home and do not really need data. Upon receiving my first invoice on the 6th of July for R386.22 for 3 gig, i contacted Autopage and spoke to Nomsa and advised them I'm not willing to pay this as it is not what was agreed upon, they promised to listen to the initial telephone call and phone me back within two days this was on the 7th. Nobody contacted me, and on the 15th i received a new invoice again for R386.22. I will not pay this, and will rather return the device and cancel the contract. My phone calls are also recorded and this is not what was agreed on. Should i not have feedback when the debit orger goes off, i will return the debit order and manually pay R79.00 over to Autopage