If you pay your energy bills by DD, do you check your energy bills when you are sent them or do you just file / delete? I will admit that I did not check mine until earlier this year when my bills seemed weird. Too hard to explain. Turned out that they had been estimating my bills for 4 months even though I have a smart meter. They tried to reduce my DD to something silly which I knew was wrong so I changed it back. Then when my contract was up they used this ridiculously low figure to give me suggested new tariffs with cheaper monthly payments. I did my own calculations and shopped around and left them.
Today I got my final bill and I appeared to owe them more than I expected. I checked my bills and discovered that my DD for 2 June was not showing on the bill even though it was on my bank statement.
British Gas tried to steal £170 from me!! I have already contacted them and will hopefully receive an amended bill.
Warning, check your bills, be smarter than them.