As per my agreement with Russels, they are changing my debit order date resulting in a negative payment review

My grandfather (ID: ********** 078088)bought me goods at Russels a while ago, I am also paid up on the account and now all of a sudden my debit order is not going off when it is supposed to. Last month, my debit only went off on the 30/09/2017, this month I called in to find out why it is not going off and the lady and she had the audacity to tell me that the bank must have rejected it, I was like "REALLY" I would have received a notification. She then goes on to tell me that since September the account has not been paid when I got the notification that the account has been paid. This is now an inconvenience as I now have to into a branch with my bank statement in order for them to rectify the problem. I feel that Russels has breached the contract with them as they have been debiting my bank account all along on the 25th of each month and now that I am nearing the end they are playing around with my payment dates in order to add on unnecessary interest. Why do the retailers do these things???