Re: Spam calls
"The telco has records of at least who it took the call from."
The scam calls coming from out of country are commonly routed through multiple and varying systems, so all the receiving Telco knows is which telco handed the call to them and bills them or logs against reciprocal agreements. Depending on how it was routed, the originating number may no longer be attached to the incoming call, or it's injected into the local recipient telco from a VOIP system with no idea where the call originated. On the other hand, I notice the scam calls randomly come from "UK" numbers where the STD code doesn't even exist or from "local" numbers in my STD code, but on the rare times I tried calling it back, got a "number unobtainable" tone. So blocking invalid number might be an option, except where genuine overseas calls come into the UK from systems that don't present CID or calls from organisations that have broken PABXs not presenting a number, eg Hospitals and Doctors surgeries, as sometime gets reported here.
I think the only real solution is your suggestion of blocking, but it would have to be blocking the previous telco or VOIP system down the line until they clean up their act, ie forcing them to be better partners. But again, it's going to be Whack-a-Mole and BT and others are unlikely to want to block a major foreign telco.