I cant downgrade my iCloud storage

I’m only using 59.2 GB of storage and I’m not able to use the 200GB plan? I’m trying to downgrade from the biggest plan which is like 2TB for $10. I don’t even use nearly that much data and I don’t earn enough money to pay that much each month for something I will never use. Someone needs to figure this out for me because this is stupid, please help.

[Re-Titled by Moderator]