Incorrect fibre billing

I have installed fibre last month, it was installed on 15/07/2022. When I took out the contract I was advised that it will only be activated once I call in to activate, I will then pay a prorata, which I wanted to only do at the end of last month due to me still paying another service provider. I phoned in on 27/07/2022 to activate. When I received my invoice at the beginning of this month I seen that it was incorrect, I phoned the fibre department and they said that I have been prorated from 15/07/2022, which I did not want. I also did not use the service from then, I only started using from 27/07/2022. They logged a discrepancy and I was told it will take 24 -48 hours to resolve, when I phoned in today I was told that it has not been resolved and I must wait up to 14days. I want this resolved before my debit order goes off on the 20th.