Just like Path did. [0] Oh dear.

[0] https://www.theverge.com/2012/2/7/2782947/path-ios-app-user-...

Telegram seems to do the same. They keep contacts which I had long deleted, even after reinstalling the app.

Yes, after prompting for permission, and explaining why. What’s the issue here? How else would they do it?

By uploading the hashes rather then the actual phone numbers.

Phone number hashes are reversible because the space is too small.