Requested Banking Details to be changed, but it was NOT implemented

I contacted Dotsure last month to change my banking details. The agent advised me that this will be implemented however on the 30th, a debit order from my old account was done. I had to pay for this debit order and thus also caused me financial inconvenience. I called thrice today, today; the first time agents were unavailable as they were busy on calls. The other two times I was directed to the incorrect department where nobody could assist me. I asked to speak to a manager however I was advised that this could not be done!