Mercides Finance Overcharged Me

I purchased a vehicle from Mercides Benz Bedfordview. My first installment according to my agreement was supposed to be R12290.00 per month for a 36 month purchase. This month I was supposed to pay the first installmemt. I got the invoice from their Mercides Finance Department for R19987.80. I called them immediatly and told them to rectify this on the 12th of September.2019. I was called today to say sorry they made a mistake and that the contract was correct for R12290.00 amd this was going to be sorted out. Tonight I looked at the business bank statement and they have taken R19987.00 from my account. This is disgusting because you are inefficient and irrisponsable with my finances. One budgets what one has been told to pay according to the contract. My sales person was Asya at Mercides Bedfordview. She also called me to apologise this morning but still NOTHING WAS DONE. To rectify this mistake. Maria Avraamides Holistic Emporium.