This may be because the hosting has expired without a payment for renewal. What can we say? We have usually sent several requests for payment. We could send around a gang of sweaty tattooed heavies, but why should we bother?
Hosting can also be suspended if the website is found to be sending unsolicited bulk emails or other breaches of our Acceptable Usage Policy.
Exceeding the bandwidth quota will cause automatic suspension, but there are usually warnings before that happens.