Wesbank not collecting monthly debit order!!!

For the past three months I have had to call Wesbank on a monthly basis to request them to collect the vehicle finance payment via debit order. I have received assurance on all occasions that it will be done, but another 25th of the month has come and gone without Wesbank debiting my account. What is even more unfair is that they keep adding interest on the outstanding amount, and yet they are the ones not collecting the money even though it's there, just waiting for them to debit as I also use FNB - just like them! I can only imagine what it is doing to my credit record! Can someone please correct this as it's costing me a lot in interest every month. If my account goes into arrears you will be calling and harassing me asking when I will be paying the money, yet I have pestered you many times and given you permission to collect the money directly!