My icloud storage was suddenly became 200GB but i didn’t pay for it, what happened?

Hello Sagwajoa,

Are you part of a Family Sharing group? If so it's possible that someone else is signed up for iCloud+ or Apple One and is sharing the allotted iCloud storage with you.

This page can help out with providing helpful info on sharing iCloud+, so that you may double-check to see if that applies for your situation: Share iCloud+ with your family - Apple Support

Cheers.