TTS777: Can anyone recommend a good software I can install on my laptops to monitor my daily usage?
Your first step is to talk/write to BT. You mention a 473MB download. The usage will also measure uploads and updates. It's important that you measure things in the same way.
I expect that BT will be able to point you in the direction of software that will measure the usage in the same way as they measure it. Often there will be something on an introduction/installation CD.
After 18 days, it's likely that you've passed any cooling off period and are in the contract for the term. Details about your obligation will be in the agreement but it's possible that BT will ask for something close to 15 monthly payments to cancel. Again, it's BT that you need to put this question to first.