You should be able to access your bill, and recent calls, via bt.com.
It's all a bit confusing for us, without the specific details (e.g. the numbers used - feel free to leave off the least few digits - times and durations of calls, etc.) but this may be telling:
whitespace wrote on Jan 1
st, 2010 at 12:12pm:
but as I had had to dial this other number,
If you dialled one number and it told you to redial another number, and you hung up and did so, then that counts a separate call, and would be charged separately. If it just said they were forwarding you to another number, and you didn't actually dial the number yourself, then AFAIK there is no way for you to be charged for it.
As others have noted, BT include calls to (most) 0845/0870 numbers within the times of their call plans, but not to 0844/0843/0871/0872 numbers. If you dialled one of these, then you would be charged for them.
If you can recall the exact sequence of events, then that may allow us to advise or explain things further.
HTH.