If your account has been Hacked or Infected you should perform following steps to fix it and secure your account.

Check if the script you use for your web site like wordpress, Drupal, Joomla etc. is up to date. You must update it to latest version.
Hacker may upload php shells in your account public_html folder to [...]

If you know of someone who is abusing the system, spamming, etc, please report abuse to abuse department of that hosting company. If you are not getting reply from hosting company, report abuse to registrar of that domain name. You can find domain registrar of the domain name from whois details.