********** deduction months after the switch to prepaid from a contract

I switched over to prepaid from contract as soon as my term expired. My last bill went off and I have not been charged since (rightfully). Today, 12 June 2022, months after my last bill went off I was charged R599 yet again. The funny thing is this isn't a singular incident as my sister had the same thing happen to her as well. ***** and *******ion is running rampant in this company.