Incorrect billing

I spoke to a sales rep to upgrade my fibre line on the 18 September 2023. I was advised that if I signup for a 12 month contract I will pay a discounted rate for the first 3 months which I agreed to. After signing up and received my first bill I then noticed that I was double billed one bill for my old fibre line and another bill for my new line. I then contacted Vodacom to sort out the issue and was advised it was an error and they will log it with their accounts team and further told it will be resolved within 7 to 14 working days. This issue has still not been resolved and its way past the SLA that was provided. Every time I call the contact centre I get told they waiting for the credit approval