iCloud storage downgrade

Someone posted they had talked to Apple Support and the check indicates it is downgraded, but you can't click Done because you still have an active subscription. You can contact iTunes Support if you want to confirm that. Either use the form or scroll to the bottom of the page in the 2nd link. Follow through the screens to get a chat or telephone option.  You may need to pick a problem that is slightly different than yours to get a chat option.  

iTunes Support – world wide

I have seen this situation lots of time. Apparently you cannot press done because the storage decrease will not actually occur until the end of the current billing cycle. I cannot say why things are set up this way.

There should be no addition charge.