Another thought... From what I can gather, you have been paying a fixed DD of £77.60 per month since your contract started in September. Your account balance on 22 Jan was only £11.50DR. That would suggest you are pretty up to date with things and there's not much wrong with your account to date. Would you agree with that or do you think there are some past problems? Your only concern it seems is the estimate of your future usage, which we think a variable DD might sort.
Are you still on E7 or are you on a single rate tariff now? It's just that when you phone CS tomorrow you might just like to confirm your tariff is as you want it. Good luck and please let us know how you get on.
I'm an Eon Next dual fuel customer with no particular expertise but have some time on my hands that I am using to try and help out a bit.