QC

I have switched servers but the old host deleted my site before they should have.
They said to let them know 2 days in advance so I did and figured that is when they would delete my site but after I sent them a cancellation notice I was sent a letter by them don't worry we will delete it later tonight or so I emailed them before they did and asked them to leave it running for anothe rcouple of days but they either never looked at the mail or whatever.
Anyway they started using my domain name and posted a page for them and their sponsors on it so I complained to one of their staff about and he apologized and tells me they delete sites asap to make room for others.
They thought I had back up files and they were sorry if I didn't but I did so I didn't mind it at first until they used my domain name for themselves.
Anyway he removed the page and made it just a plain 404 page but now today I see are using my domain name agin for a 404 page with their ads on it.I don't like it because it can mess up what little reputation my domain has out there but I really want to know if they are allowed to use domain names that aren't theirs to begin with unless given permission?
QC