This is a basic ISP, obviously any spam is coming from customers, who happen to own subdomains or IPs. The subdomains in particular should receive the bad rating, not the ISP.
The only time an ISP should get bad ratings for it's customers' spam is when a "bad customer experience" is the result when of to notify the ISP of said customer.
ISPs should not be held responsible for their customer's actions unless they actively avoid taking action when complaints about their customers spaming come in. (Such ISPs do exist. Some seem to make a business of turning a blind eye to spammers and even black-hat hackers buying server space from them.)