Wow, sounds like quite a ride you've had. It seems a case of pure bad luck from what I can see. Personally, I think that you're right in just wanting to move on. I don't think the lady meant to cause any negligence - after all, she wouldn't have paid the vet's fees if she didn't care.
Doesn't sound like much fun to be fair mate. It's always hard when cats go missing, I know how it felt when mine went missing 13 years ago. Considering how small the are, they don't half leave huge paw prints in your heart when something happens.
There have been a few reports of chipped cats being claimed and not returned to their owner in the media. I don't think it proves absolute ownership. https://www.thesun.co.uk/news/15950...-cant-be-told-who-because-of-data-protection/ Excuse the sun link. My rescue is with reg with petlog