http://www.spamhaus.org/ The Spamhaus Project is an international nonprofit organization whose mission is to track the Internet's spam operations and sources, to provide dependable realtime anti-spam protection for Internet networks, to work with Law Enforcement Agencies to identify and pursue spam and malware gangs worldwide, and to lobby governments for effective anti-spam legislation.
They really monitor bad spammers - you do not want to have our IP Range on that list.
If it gets there many sites and networks will block your ips' and they will become useless
We can help you get them removed, and only if you tell them you have eliminated the customers, in which case we can clean your IPs.
That said, it takes us time and time is money, so if it is a simple remove and you can somehow do it yourself, no charge, but if you need us to help, there is a $100 fee.
Choose your customers carefully, spammers are bad guys and do not like to pay, and they will cost you money, they might not even pay your bill, it is bad to work with them.