Edf bill recalculation for entire period

albu

I switched to Eon from EDF. When EDF sent the last bill they changed my meter type from Standard to Economy 7 and did a recalculation for my entire period with them (about 1.5 years). The bill shows that I need to pay about £500 – they put the same meter readings on day and night and are charging me twice. I called them and they changed my meter type back to Standard and send me another bill. This time my bill is £125.
I checked meter reading from my previous bill and the closing meter reading. This is a period of three months (June-August). For this period I used 784 units and also paid £105 in Direct Debit. I did a simple calculation using the same tariff they charged three months back (the tariff didn’t change for this period) and 784 units cost a little bit more than £100. Also I was £6 in debt three months back (based on the previous bill). This looks like I should pay around £106 and I paid already £105 in DD which means that my last bill should be not more than £10-20.
I called them to discuss this but they kept telling me that they did a recalculation for entire period because the meter type was changed to Economy 7 and back to Standard and the bill is correct. This seems to be wrong for me because I was on different tariffs (for a year I had Online saver4 which was a cheap one) but now they do the recalculation using only one tariff which I believe is the highest one. They failed to tell me what tariff they used to do the recalculation. After a few calls they told me that they did another recalculation and now the bill is £94, however this seems to be wrong because it looks like 784 units costs about £200. In the previous bill I paid £150 for about 1600 units.