God BT are such a bunch of b*stards!! I have prob been on the phone in total about 10 hours over the past couple of months, all to do with just setting up a dd.
Anyway if some people have said to you that you shouldn't be charged, I would ring again the customer services number (you'll probably have to hold for over an hour), then demand to speak to a manager. Don't bother with a complaints team - they don't exist and we just kept getting cut off. When I actually got a senior member of staff he sorted out my problem and arranged a credit for me.
I am still in the process of complaining about my wasted time, and the cost of the calls to their customer services number (�40 in total because I rang off my mobile) but if you can get them to remove the charge from your account that would be a start.
Good luck - I would suggest contacting their regulator OTELO about this, whether they credit you or not. If it comes to it I would pay the fee but then keep on at them to get it refunded.
I hate BT so much - they are the most useless excuse for a company, but unfortunately I have to be with them to get Sky!