change of bank details

i have been trying since Friday to change debit order details. the call centre said I must send 3rd party form to the debit order department and it is still not change. apperantly they say it can't be viewed. I must do it in pdf format when it is in pdf format. their service is really getting pathetic. as some people do not get the proper training. and on top of that they say you can change your details on self service which is never working.... they tell you everytime they will esculate the problem and on the walker everytime we need to phone them to reset device and send a signal... so what is the point... it is not the service we pay for...