ABNORMAL LOAN CHARGES

I took a loan from Old Mutual in 2020. I have been making payments all the time until today. I realised that my balance is not stable and the amount is going down, up and down. In 2022 November my balance was R147 487. 00. I requested the statement last week on the 24 July 2025 and my balance is R132 653.80. I have been calling to seek answers and I was always told the matter will be escalated for investigation, but nothing has been done. I wrote emails and i was given a number to call, where there is no one to talk to me. sometimes it just rings and drops. This is very frustrating, and I need answers from the bank. I also previously had unknown debit orders and when i report them i was told there is nothing the bank will do after explaining the non-existence of such company. How do I deal with this.