I can confirm after having just spoken with XSServer support at their listed phone number that they indeed do nothing regarding spam reports.
They did mention that they forward all abuse reports to their customers, but also said that they have a lot of spammers on their network. When I asked if spamming was against their terms of service, they agreed. When I asked how they enforced their terms of service, the guy got pretty rude with me, refused to answer, and advised me to just block their IP addresses if it bothers me. However, no action aside from possibly forwarding abuse reports to their customers is taken by XSServer. They are definitely a spammer haven, which is likely why no response to abuse reports is ever received from them, they are well aware of the spam coming from their network, and they intend on doing nothing about it.