Different interest rate than what i initially signed for

I am not happy with ABSA vehicle finance, I signed a contract with an 11.750 interest rate and was given a 13,8 interest on my statements letters and because of that my installment became very high. when I initially signed the contract the installment I signed for was R6277.44 and currently, I am paying R6 800, I keep calling client service and was told my issue has been handled, I was refunded R1000 but my problem got worse when I was sent an SMS to confirm that another debit will go through on 31/08/2022 while my normal monthly debit order had gone off on 15/08/2022. I have sent multiple messages to complaints and nothing is resolved. When I call client service they hang up and can't answer my questions. How can an account be debited twice in one month? Right now a debit will go off on 31/08/2022 and my account will not be having money which will affect my credit record. I requested someone just to call me and explain why I am not getting what I signed for and for someone to explain my sudden elevated installment, but no one is assisting me with my query . Although I am enjoying my car, I am very unhappy and disappointed with ABSA.