For years my monthly DD has been on the 15th of the month.
This month my 'Dashboard' shows money paid on the 12th whilst my bank shows debited on the 13th.
What next, can BT just change the date anyway they choose without notification at all?
Probably as the 15th is a Sunday so DD is taken on last working day before 15th hence 13th according to bank
That is probably true, but when BT ceases to send me the monthly emails and they always said that the DD would be on or after the 15th.
This email was dated the 08/07/2019 14:10 and also says;
"You don't need to do anything to pay it. We'll take your Direct Debit as normal, at least eight days after the date on your bill"
Please note the 'at least'
The bill itself will indicate when payment is scheduled to be taken ("on or after ..."). If the bill has already been paid, the online version will show the next billing and payment dates.
There are regularly discrepancies between payment dates online, I suspect because the DD beneficiary uses the date taken while the bank updates statements overnight. Eg, my bill this month states payment on 4th while bank statement says 5th.
Can't see any reason why you should have been debited before today. As already pointed out, that's obviously during the weekend but, in my experience, on those occasions payments are invariably taken on the Monday.