I can’t downgrade my storage plan

Solution: I went to http://reportaproblem.apple.com/ and chose to report a quality problem with my iCloud+ 200 GB plan, then explained I wanted to downgrade to 50 GB. Apple got back to me within 24 hours and canceled and refunded my 200 GB payment, therefore switching me over to the 5 GB free plan. From there I was able to upgrade to 50 GB without losing any files (since files are saved for a couple of days even after you’ve been downgraded to the free 5 GB plan).