Wrong billing and wrong contract

I signed in for Wifi ref number RAU025 on 26/06/2023 for 4Mbps at R499 per month. Already end June R999 was deducted from my bank account, and another Invoice sent for 1 Aug 2023. This is *******. Daylight *******. I phoned, they promised to phone back, but no calls received from them. I Want them to change the Aug bill to R499 and pay me back the R500 that was overcharged in June. As a matter of fact, I paid the June bill in their shop. So, they must pay me back R999. How can they try to rob pensioners? We have limited funds to live off, and try to work within our budget. I also paid R1500 for a receiver that was already installed in my house. R1 999 for June Wifi R499, and R1500 for the receiver. What is wrong in this country???