Debit order date unchanged after two cycles

I contacted absa on the 7th of May to let them know that I need them to change the debit order date for this account. The reason I said clearly is I am changing jobs and will no longer get paid on the 20th. On the 20th of May I get a debit order, I call them they say they don't know what happened. They can see the date was changed and will call me back with an explanation(they never did). On my internet banking transaction history you can see clearly on the 7th of May( Change of Due date) This Saturday 20th of June again I get a debit order on my account. I am not sure they understand how doing such affects ones credit rating. I don't have enough money in the account and right now sitting on negative.