Bad service

I recently got car finace through Wesbank. The contract was signed and it stated the first instalment is due to go through on the 25th of April 2018, a debit order has already off on the 24th of March. This is unacceptable as a contract was signed and now they have gone against it, I have been calling for three days and no one can give me an answer. I want a refund immediately as this is their fault.