We use some blocklists with the mod_security setup to help prevent spam/illegal activities on sites hosted with us, I don't know exactly what lists we do use however, but I'd guess the one I found your IP on is one of them.
I did look your IP (the one you posted on these forums from) up at
https://www.spamhaus.org and I found it listed on one of the blocklist on their site when checking.
The good news is that the ones that have your IP listed does have a self removal tool, just click the link for the specific list on that site.
Ones you have completed the removal steps you just need to wait for the lists we subscribe for to be updated so it would likely not be immediate, make sure to take proper precautions to not get listed again as well.