They told me direct debit would be automatically canceld after last month of payment about £40 and then tried to take well over £500,luckily I didn't have that amount in my account so they didn't get it but they tried a couple of times and when I found out I cancelled the direct debit,if I were you I would cancel direct debit and send them the 10 days owing by check , postal order or even registered cash be very careful at end of contract because they try to say something like there was unexpected charges so we just took it,in my case it was an error by bt but it would have taken a crowbar to get it back once they had it,also they can destroy your credit rating without telling you or asking anyone else they just do it,keep a close eye on this as I've been dealing with bt mistakes for ten month's and it's still not resolved
The BT billing system bills in advance and doesn't factor in any pending cease requests, let's say it's June and a 30 day month, so if on the 1st of the month you give 30 days notice, the service ends on the 30th.
If your billing cycle is the 15th, you'll be billed until the 14th of the following month, which by the example above means you'll pay an extra 14 days, once the final bill generates 7 days after the service ends, you will be refunded the 14 days back into the bank and then the direct debit is cancelled.
I would caution against cancelling the direct debit. If BT go to get the money and the DD is cancelled it will be classed as a non payment which could lead to problems.
It is unlikely that BT are making much if any money out of having your payment for a week or two. The reason that it is done in that way is purely the billing cycle.
I know what you mean but it's how BT do it, if it did factor in the cease it would be easier for you, however some customers then decide a few days before the cease that instead they'll keep the service, you'd then end up with a 6 week bill the following month.
Although just as you've done, cancel the DD and pay the bill manually, I'm not sure how that reflects on your credit file though, again using my example above, that would mean you'd be over 2 weeks late paying the bill,
however I'm far from an expert with credit files, perhaps it has no impact.
*Edit* @gg30340 replied before me.
If you type bt t&cs in Google it will tell you on section about payment,they are supposed to send letters reminding you of any outstanding money owed and about two weeks after that they start looking at it so about a month before they think about debt agencies, so by the time you manually send final payment you will have plenty of spare time,recorded post is about £1.20,read the t&cs because it set out there obligations to you because a contract is not a one way street,I don't know why the experts are not telling you this as you obviously don't want to pay money you don't owe and t&cs will give you correct info for your issue
This is quite common so it isn't just BT. Personally I don't see the problem, for example if you were to make any chargeable calls or purchases the day after your billing date then you effectively are paying for them a month in arrears. They do not request immediate payment, and if a customer makes regular chargeable calls they average them to give a regular DD payment rather than bills spiking.
Utility companies do the same and depending upon when you switch suppliers, you will either be paying significantly upfront or in arrears.