Overcharged bills by energy companies

Hi there,

My friend was horrifically overcharged by British Gas- they took out £1000 from an account and then overcharged them for their closing bills. They kept changing the times when the readings were from and sent different bills for the same time period.

Has this happened to anyone else? There's a theory that this seems to happen more to younger people but would be keen to hear if that's the case.

Thank you