What should an "average" 2 bed bungalow DD be?

macman

I don't understand why the account is not accessible to you? Is the other family member not willing to let you view the account? You don't need to speak to EDF, you just need to log into the online account and check your previous bills and statements to see what your actual usage is and whether your bills are actuals or estimates. You've clearly put a lot of work into the other issues here, but unless you know what you are actually using then you can't hope to resolve this problem. If you are going to request a lower DD level from EDF, then you first need to know what it should actually be set at by doing the maths.
To emphasise, so far we don't know either your kWh usage or your tariff unit rates and s/c's).
Likewise, your C Tax online account will clearly show if you have received the £150 rebate or not-you should have had that months ago if in Bands A to D. The WFP is based on your age at qualifying date, not on retirement age. You need to have been born on or before 25/9/56 to qualify this winter.
If in receipt of D|LA or AA then another £150 should have been paid in September.