You're going to have to work this with the Abuse department. At least you say "suspended," rather than "terminated."
Spam abuse usually happens one of two ways:
1) You have a mailing list on your domain that's not double-opt-in (i.e. Someone requests it, then confirms their request)
2) You have a formmail type script that's been exploited.
In these two cases, Abuse will usually want you to close the hole first before they reinstate your account.
Sometimes someone just complains about spam if you do a Reply to All and someone just clicks a Spam button because they're lazy or don't know any better. This usually isn't enough to get your account suspended.