Best answer by woz
again forgive me for any assumptions but I'll add to Stephen's excellent reply.
When you joinyour direct debit amount is set on the assumption that you will use a certain amount of energy over the following year. Of course that is a guesstimate, and will almost certainly never work out exactly over a year but it c=should be close enough not to matter (more of that later).
Your monthly amount is always set to pay for a full statement month - no matter when you submit the readings. If you submit right at the end or near the end of the month (a couple of days after you get the reminder) it will be absolutely accurate, but if you submit a few days or more before your statement date, the few (or more) remaining days to your statement date will be estimated (usually so close as to not matter at all - the more days estimated the less accurate it will be but that doesn't matter.
On your statement you will see the readings you've submitted plus the estimated few (or more) days up to when your statement is produced.
That is what you are charged for, the DD payment is first paid at the start of the billing month, (you can set the date as you wish thereafter) the charges made at the end, and deducted from your balance, leaving you with what's left plus any payments from the next DD that Pure Planet have received.
The reason the estimated days don't matter is that the next time you submit readings any discrepancy is corrected.
If your original estimate is close the statement balance will drift around an average months payment, but if it consistently rises or falls over many months leaving you with a balance much in excess of a months payment, OR very much lower, then the DD can be adjusted (with your agreement) to bring your expected balance back on track. As said you ultimately will ONLY ever pay for what you use but your balance will drift around depending on the weather and your usage.
Does that help at all?
Am I being charged an accurate amount based on my readings?