LIR stands for LOCAL internet registry, not LEGAL, and has to do with handing out of address ranges. It doesn't imply providing transit or any other service. Curious that a director of such an outfit doesn't know this.
Spamhaus say they've repeatedly notified them and A2B say they only got one email after asking for it. Time to whip out the evidence. Spamhaus does, as per their published policies, move up (first one, then) two ISPs if the ones below don't react. Again, time to whip out the evidence. Making a point is exactly what spamhaus is about. It is why they only publish blocklists that others to use at their discretion.
This is perfectly reasonable in the cooperative of networks that forms the larger internet. Collateral damage is implied in the escalation policy, but A2B or whoever could've moved the innocents to clean blocks (and if they had run out of addresses, weren't they a LIR?), so it's their failure to care for their network that's gotten them into this. Shoulda moved addresses around, or better yet, not host known spammers. They should have gotten ample advance warning. If not they might have something to take up with spamhaus.
Who else supports A2B's cause? Er, their so-not-a-subsidiary-honest Datahouse is probably one (say hi to the sockpuppet) and well maybe CB3ROB is the other. Though getting classified as "dutch" ought to upset them a bit unless they'll argue that part just happens to not be part of their CYBERBUNKER thing. Wonder what that "strict" policy is. One could speculate, darkly, it's probably very strict on what abuse complaints they'll look at.
I think that spamhaus has the better cards in this, but with the low standards of plod and prosecutors in the Netherlands, if they do manage to get around to this complaint we'll just have to watch what's going to happen.