Man, where do I start. I'm with them too having just changed from Virgin. My online bill says it will be due on the 14th of each month. However, following a phonecall to them I learned that in fact no debit would be made until the 19th. A pity that on the 19th I had no funds in that account, although the money was there on the 14th.
I duly received my letter from the bank (BoS) stating that an attempt had been made on the 24th(!) to extract the debit, which failed. The bank billed me £35 for this priviledge. I blew a gasket. I phoned BT again ang was told that they had indeed went for the money on the 19th and that they HAD been paid. I owed nothing. Cool, I thought. I phoned the bank only to be told that BT were telling porkies. They had not attempted to extract the money until the 24th and they had failed. I refused to pay the banks fine and they suggested to me that I phone BT again and tell them about the banks version of events. When I again phoned BT I got a different person. Of course. This persons version of events concurred with the banks version and she had no idea why I had been told anything different by another member of her staff! I was asked to get the bank to send me a statement, which I had to then send to BT so that they could pay off the fine I didn't incur.
Now that I'm writing this down i'm not sure any more if these events are in the same order. I'm seriously thinking of going to live in a cave.
If I was you I'd set up your direct debit from an account that always has cash in it. At least that way you won't incur any charges from your bank.