Who's fault is it?

I have a problem with absa I bought a house in 2012 in Protea Glen ext26.. I made an arrangement with them to debit their monthly installment via debit order and later I changed the installment to be deducted from payslip and never informed absa that they must stop deducting via debit order now they take their monthly installment via payslip and still go to the account for their debit they don't get money and bounce and creates charges and interest on my account and was later informed by one of the absa member that I am owing and made arrangements with him and was informed the matter will be sorted out by adding a month extra on my bond and later summoned with a letter on my door saying I owe absaR5440 for the unpaid debit order with interest I feel it's unfair because I thought the issue was sorted out but not I then proceeded to the bank to cancel debit order and tried to call the home loan division but their only solution was that I pay R1800 extra on top top of my bond installment for 3months to cover the debt just because I did not inform them not to deduct from that old account anymore wondering if their system did not pick up the time I change to payslip or is it all my fault? and the saddest part is that no one called me from the first time they noticed the debit order has bounce its almost a year and half now I changed to pay bond from debit to payslip (stop order)