I saw a story a while back where someone made their personal number premium rate to reduce nuisance calls (it was successful); that may also be an option.

Not a great one as the problem is Google rather than the callers, but I guess you could also have an immediate route to voicemail with the message "this is not, repeat not, google".

Sure, $50 is enough to file a court claim saying Google owes you £300 because of the cost of sorting out this mess.

It might work pretty well, Google can choose to say oh yeah, that's about right, here's £300 or they can make this into a big deal whereupon their in-house legal team are immediately going to spend far more than £300 just showing up and making their position in court, and they might well lose if you tried to get it fixed and they were useless.