Following on from my previous post of 9 December, I then received a further electricity bill covering most of November and the early part of December, again all charged at the NextFlex rate. After lodging several complaints, my tariff was changed back to NextDrive, and since then I have received regular bills for both gas and electricity which are calculated using the correct tariff (and agree with my calculations). This just leaves the issue of approximately 3 months worth of usage which has been calculated at NextFlex rate. My calculations suggest that as a result I have been overcharged by a little over £200.
E.On's reason for charging me at the NextFlex tariff for this period was that "We tried to bill your account on the correct tariff but because we could not retrieve the half hourly readings, we had to temporarily switch the tariff so that it would not amount to a billing gap. We currently do not have the half hourly readings and as such we may not be able to recalculate the bill just yet."
They then asked if I could send them the half hour readings that I have downloaded from glowmarkt.com!
I have found E.On's complaints handling process awful and certainly not in line with the email policy they sent me.. I have generally given up phoning them as it takes 15-20 minutes for somebody to tell me tat they can't deal with this and need to pass it on to the EV team who will get back to me (they never have). Instead I have sent emails but the response time is typically about 3 days (in one case reached 9) and doesn't actually lead to any progress.
Despite having sent my downloaded data I have still not seen any recalculated bills. When my "Complaint Manager" eventually called at the end of December he was unaware of the incorrect bills and didn't appear any better informed in another call last week.
So with no progress to date, taking my case to the Energy Ombudsman next month is looking increasingly likely.
In response to @evgone
I understand that all smart meter data is collected and held by a single industry wide body, the Data Collection Company or DCC. Suppliers then access this data for their billing systems. Similarly third party websites such as glowmarkt.com can get the data if the customer gives authorisation. So in theory E.On should be able to retrieve historic data and recalculate bills if necessary. Whether they have the systems in place or the willingness to do this seems another matter.