ISP Excess Bandwidth Scam

It is with some glee that I receive an email from the errant ISP of several postings passim (identity secret for reasons given previously) stating that one of my sites has exceeded the 20 GB bandwidth limit allowed on this account every month.

Excess of 20 GB, and it's only 4 hours and 2 minutes into the third day of the month!

On further examination I find that I deactivated this website on 13 April (because of a bandwidth excess warning) and that this site has been inactive from that time until this.

So why the bandwidth use? So far they have not replied.