DEBIT NEVER WENT THROUGH

I BOUGHT MY CAR WITH ABSA VEHICLE FINANCE IN 2014 and I used my standard bank account number for the debit order, for some reason the debit did not go through on the 1st of April, I phoned in on the 7th and they claim that my account details were changed on the system to my absa account, the absa account they are talking about was closed months before buying my car, how is that, they are affecting my credit badly and I need an explanation as to why was this done