The warranty provider? Your telco? Peering telco? The data provider? The call centre?

How do you find / sue them?

As an aside: you could then easily add carriers or intermediaries to a block list. You could even subscribe to a distributed block list. You could subscribe to an always-allow list that contains hospitals, police stations, and emergency services. It'd be so much better than what we have now.

That would require some major respecification of PSTN calling standards.

That said, yes, something along these lines seems necessary.

Even automated curtailment by last-link telcos (e.g., your own telco) based on rejection / complaint rates (e.g., recpients reporting calls as spam) could be A Thing, and are not dissimilar to how email spam management occurs today. Making that the peer's problem incentivises them to clean up their acts.