In the Netherlands, Ziggo (UPC) usually cleans up the offending IP for you when you call customer support and will contact spamhaus that action has been taken.
As I suspected, there is one serious spammer in that IP block. Can be you, can be someone else in the same /24 range.(That's the resolution, it also means the spammer is likely in your immediate physical neighborhood, given the way UPC configures their infrastructure. At least on cable. Note this is not always the case, but likely the case...)
Spammer can also be read as a hacked computer....