did you manage to upgrade the storage.
I have not be able to do so, and yes I have tried all of the apple community advice.
What happens when you follow:
Upgrade your iCloud storage plan - Apple Support?
If you are still unable to upgrade you might need to:
Contact Apple for support and service - Apple Support
it is the same with my phone
I even deleted the HD
and reinstalled OS
You can try with another device(if you have)
or another card,
If you can't or it still happens:
I'm just a user like you so I don't know why it does not work for you
cool, thank you