Well keep this in mind....A reputable host will provide you proof to back their claim when asked. They won't simply shut your down without giving you the benefit of proof.
It sounds to me that you may have picked an unexperienced company in which to host your site.
Now, however, I noticed that you mentioned that your site is for sending out eZines. There is a possibility that this was misinterpreted as spam.
A lot of people who sign up for ezines forget when they do it, or may not have done it at all, and just had their email submitted by someone else. While sending out ezines is typically a harmless thing, many people who can't remember signing up for it, or those who had their email entered without permission, will immediately scream "SPAM" without asking you anything at all.
If/when your host receives a sufficient amount of these reports from these people, the host is obligated to stop the spam first, and provide answers later, as long as they DO provide answers.
It's very similar to a police officer arresting you for a crime they're not sure if you commited, but they think you may have. They will do a quick initial investigation to make sure there is enough to arrest you on (and it doesn't have to be much). They will then detain you, while they build a case of evidence and facts against you. Of course, if they can't prove you did it, they let you go free.
If you feel your host is reputible.....try to work with them to figure out what happened, how it happened, and what you can do to help.
