i don't really understand why you have been payng more than you need to? have you built up a credit? Why did you just cancel the standing order before you had set up a new payment?
Its really up to you to make sure the bll is paid, and if you cancel the standing order to make sure that some other payment is made. direct debit mandate is more usual fro ouncil tax because 1) the amounts vary by a few pence each month sometimes and 2) there are 2 months in the year you dont have to pay it