I signed up with EDF about 4 months ago and using my previous
consumption data for gas and leccy, they came up with £90 per month on a
fixed to Feb 2015 tariff. I was happy with this.

Now having read the meters, they have produced a bill showing I've paid
them £360 (as agreed) and used £136 of energy & std charges. So I'm £224
in credit.

However they are now saying based on this (statistically
unrepresentative amount of information) they are putting up my DD to
£118!!!!

HTF do they get away with behaving like this??

I've sent them a snotty email insisting on returning my DD to £90 but
yet to hear back from them.