Car finance Issue and poor service

I bought a car in Dec 2021, under finance by Standard Bank, my dealership made manual payment to my account, it took Standard Bank over 20 days to allocate the funds to my account(after numerous calls and sending proof of payment)

When I thought everything was okay, boom Standard Bank increase my installment(whereas it is suppose to be decreased because of the manual payment), inquired, they apologized they said there are fixing it.

They corrected it and sent me proof of the correct installment and debi check that I need to approve. The debit check came in incorrect, I had to decline it for over 6 times. Two months have pass with the issue being resolved.

I have engage with team leader and other consultants, they all promise to assist but nothing.

MAIN ISSUE: my credit score shows a missed payment and i am now a defaulting payer. They no longer respond to my emails.