When you say "We have been hacked", do you mean your hosting service has been hacked, or your site has been hacked?
It's an easy option to blame host providers, but it may be nothing to do with them.
How is your email facilitated? Is it through a content management system, or directly via your host providers control panel?
Spam is a problem for everyone to a greater or lesser degree and it depends upon many components any of which may have been compromised.
You need to be a lot more specific about the circumstances and consequences, but not so far as putting any security you may have in place at risk.
It could be something as simple as having a lousy password policy.