Bell doesn't offer any tools outside of their own usage monitoring tool located on their own website.
If you have a router running Tomato or DD-WRT firmwares both can track WAN usage. Alternatively you could try a free tool called NetWorx (link below) which can track usage of the computer its installed on. »www.softperfect.com/products/networx/
If you have more than one system you will have to install on each of them, then manually track the usage on each of them to get overall usage.