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SmartMeterQueries
Can you show us the actual meter readings on which billing has been based for the periods in question? How many were 'smart' readings, how many were manually submitted readings and were any actually submitted by a meter reader?
The usual reason for bills needing to be recalculated is where smart readings have not been taken so estimates have been used instead to 'guestimate' a monthly bill. If your readings have gone down rather than up, that suggests that an estimate has been used at some point, and then corrections have been applied once a definitive reading has been used. From your screenshot, it seems that estimates are being used. That happens when the smart meters can't send readings and you haven't manually submitted a reading in it's place.
You are also paying by a method other than direct debit, so that isn't helping matters. You'd pay rather less if you set up a DD, and that can be a variable DD rather than a fixed monthly amount if you prefer.
I know smart meters are supposed to make life easier and make billing more accurate, but it seems in your case that readings haven't been submitted, either 'smartly' or manually so estimates have been used in their place. Add to that the changes in tariff every quarter (assuming you are on the variable rate Next Flex option), that creates a whole can of worms with recalculation if you don't provide accurate readings on cap change dates (01 Jan, 01 Apr, 01 Jul and 01 Oct).
I don't have a smart meter, but I submit manual readings every month without fail. Even folk with smart meters still like to submit manual readings quarterly to make sure the billing is accurate when the price cap changes. Smart reading scheduled dates rarely coincide with tariff changes.
Go into the meter read history on your online account and see what the reads say (SMART, Estimate or Manual). That will give you some idea as to what is transpiring.
My meter read history looks like this and you can see estimates have been used on occasion, but an accurate manual read will get things back on track very quickly. As it happens in my case, E.On Next are far more likely to actually underestimate than overestimate!