BT continues to charge me even though I switched provider using OTS.

400ixl

You did the right thing in not cancelling the DD as that could have left you with a missed payment marker on your credit account.

Get the final bill sorted and if this is less than your DD they took then get the refund issued and accept their £20.

phillw

I'm not sure they could get away with leaving a non payment marker, if you didn't owe any money.

But I'd certainly raise a direct debit indemnity claim for any money outstanding and ask the bank to waive any fees. I find that most banks are pretty amenable, if you ask nicely and say the right things. I have mobile alerts setup, I argue that I didn't receive it (or I wouldn't have gone ove drawn)

The £20 is pretty good for BT, they don't like giving out compensation.

amit1985

Update.
They have closed my complaint as they say I haven't been in touch with them since I raised the complaint. Since I opened the complaint they emailed me twice to say I don't need to do anything as they are looking into it and will be in touch, which they haven't.
They still haven't closed my account and continue to bill me. I have cancelled my DD so they can't take any money but now send me letters saying I have outstanding bills that need to be paid. 
I've tried to talk to them again and I just get thrown to different people. Who knew moving broadband providers would be this hard!