A girl called Kate whose family were clearly like the richest poshest people I'd ever known, in Oxford of all places.

Something like this:

Pretty sure I was 15... A girl called Kate

By the sounds of it, did she by any chance end up marrying a guy named William?

Oddly her phone number is the only one I remember other than my own current one.

I remember a few childhood numbers - barely my own now.

This story takes a dark, creepy turn though.

This definitely needs some light of Chain!