Incorrect data charge

On the 21/11/2018 I went to MTN to do an upgrade to a SIM only data deal which was part of black Friday data promotion at R199.00. On arrival the system was very slow and the agent by the name of Thabo requested that we signed the paperwork and he will capture it as soon as the system is up. We did that and left everything into his capable hands. The sim only deal included 10GB anytime and 10GB night and 14GB Free pass for 12 months. In December when I received my statement I was charged R299.00 instead of R199.00. In January I contacted the customer care and I was advised to go back to the dealer where I took the contract. In February I went to the dealer and inform them about the billing issue. A call was eventually logged on 14/03/2019. On the 27/03/2019 I received an SMS stating that my query has been resolved with referenced no 1- ********** 9141. On the 15/04/2019 I was still charged R299.00. On the 03/05/2019 I contacted the store manager who informed me that the agent did not log the refund ticket hence he will log it and once and come back to me. I waited for the call and on the 06/05/2019 I went to the dealer again as I did not receive any feedback from him. On arrival he was busy with a client and I spoke to the agent Thabo and informed him what the manager said he was supposed to do, he promised to do a follow up on the matter. Up to date no feedback has been received from MTN and I am still billed R299.00 every month.