What a disaster to change banking details

We have change to a new bank and we have changed our banking detail at Autopage, but because of the time of the month it was not loaded on the system to run for the next debit order, so I had to make cash payment. After it we went in and asked again and it was correct. Then only the half of the contact amount was deducted, and we phoned in and they said that the handsets were paid up, that is why the amount was decreased. One month later we phoned in again, and then it was changed to the original amount, but now it has changed from debit order to a cash payment. No one informed us about this change. There were money in the account, no debit order were send back, and we were informed about it when my son wanted to upgrade, and he was told that there were no payment made, so he made an cash payment. I'm furious! We have this contract now for more than 8 years, and to be informed that we have a bad name, and he cannot upgrade because the system will not approve his application. I want to know who is responsible for this mistake. I did phone in and spoke to Samatha, but she said there is no fault at their side. On my account it is stipulated that this account is a cash account.