debit order date changed without my consent

Standard bank changed the debit date without confirming with me. They deducted my loan on the 14th instead of 15th. I had money for the full tank for fuel. Only to realize after pouring that my account has a negative balance. I called and could not get help. The only available option was to increase my overdraft facility, which will mean that I have to pay an extra interest. I'm very upset. I had to leave my phone in the garage and get if after paying and got late at work