Overcharged invoices

I called into rain at the beginning of June to make a cancellation for my 4G plan and to upgrade to the 5G home WiFi. I paid a discounted price for the home WiFi and paid the full amount for the 4G plan (which was supposed to be my last payment) when I received my invoice for July I noticed that I have been overcharged , it been 2 weeks since I requested a call back to clarify why I have been charged so much and yet nobody has bothered calling me back. It seems like existing customers are not a priority for rain