I haven't checked the date of your post but I'm having a similar problem. I share a house with others and we have unlimited broadband which was set up for someone that was using a lot but was willing to pay the extra which was fine. What has happened now is that the land lord wanted me to share the cost of the package which I refused whereupon he said that I was limited on the amount of Gb I could use, fair enough so as long as I don,t go above the 10gb limit I wont get any arguments. So the bt usage monitor would have been very useful.
However When I was on a 10gb package and living with others and we had to be careful about exceeding the limit I downloaded a meter. It was called 'Tautology bandwidth meter v1.8' sorry but I don't have the link but you could look it up. I have to warn you though that this will only monitor the pc or whatever you're using. When I changed my computer I also copied the files to my new one and I have just fired it up and seems to be working fine so it's quite a robust little program, it was free as well. Maybe this will help albeit a bit late perhaps. If you ever get this.