I missed the bit about the planet. I'd echo fusionx's statement. The planet is a large reputable company who rent dedicated servers (one of its subsiduries is servermatrix.com) both are big names in the dedicated arena.

I've know the planet to pull the plug on email spammers very quickly, the last thing they want is a block of their ip's on a blacklist.

Kgun you could try contacting the planet with the ip's you have and they can narrow it down for you to see if it is a single user on that server or if it is a webhosts server they can point you at the person to contact and they in turn can narrow it down to a single user.