Website Hacked Reinstall a no go....

Okay, we are pretty sure our website is/was hacked. mommy-talk.com smf is our host. They are no help either. The only thing they could recommend was reinstalling. We reinstalled and the main admin's account was hacked afterwards. Here is what we have done so far...

1. Changed all passwords
2. Reinstalled
3. gave no permissions to the main admin person
4. then she created a new ID under a different ID, pass, and email. (but same IP)

We are pretty sure we know who is doing this. Is there a way to stop/block the IP? Thanks in advance!