Best answer by woz
you aren't being overcharged unless your direct debit is wrong. Your quote was based on the usage over a year, but you pay more in winter and less in summer months
Your payment will reduce in April.
If annually your estimate was £1200 with PP you would pay £80 April to Sept and £120 October to March, but with a.n other supplier where payments were the same every month you'd pay £100 every month (so PP would be £20 less in summer , £20 more in winter)
The above is assuming your estimated usage was correct, but it might be wrong in which case you need to discuss that as suggested.
I switched to Pureplanet in part to reduce my costs, as money is tight, but am being overcharged every month, leaving my account massively in credit. Could the monthly direct debit be reduced to a more realistic amount?