App Payment not Allocated causing unfavorable conditions & a bad record on my credit bureau

Cell C has been giving me issues with updating payments. I made payments in June 2021 via their app its now August and that payment is yet to be allocated correctly. I keep on getting sms's stating I have arrears yet I have made several calls to its call centre regarding the same issue. Now my sim card is suspended yet I didn't cause the issue. Was it Cell C's way of de*****ing its clients by creating an app that has an option to make payments with when they knew very well that its not in sync with their billing system. I'm furious cos it's over a whole month & my credit score is being affected by this problem. I feel ****** cause they still demanding a payment that I've already made. WHY?????