Second, note that unlike with ipv4, for ipv6 SBLCSS lists subnets, not individual IP address.
Moreover, SBLCSS is a supplementary list, it is not meant to be used as a [sole] RBL, so you might be looking at someone else's configuration issue.
This implies that they have some kind of blind listing, either completely random or they use some kind of subnet reputation.
Not much that you can do, just visit their site and request a delisting.
Not fair that they blindly go around listing addresses that have not email capability, or aren't even assigned to a server, poor judgement and implementation on their part.
All my Linode IPv6 addresses (including those that don't send emails) are listed by Spamhaus. I requested delist, but a few days later, it's on the list again.
Google postmaster tool also tells me that my IPv6 address has bad reputation. I don't know why, because I use both IPv6 and IPv4 address and the IPv4 address is in good reputation.
I guess I will no longer use IPv6 to send emails.