Telkom Mobile can't explain why they overcharged me

I have a cellphone contract with Telkom Mobile since October 2018. I have never skipped a payment ever. I was debited an additional R230+ in March 2020 and have had no joy in getting this sorted. A consultant on Twitter told me that it was because I had skipped a payment in January. I literally sent her back 6 invoices dating as far back as October last year. My subscription has never been disconnected. I received a reminder sms of the next debit order that's going through in a few days yet I still have a complaint that was left hanging. I want my money back. It can go towards paying my subscription next month if you cannot return it to my account but something needs to happen. I just cannot wait for this contract to end as well so that I can just find a better service provider.