Frustration with iCloud storage purchase upgrade

I appear to have been caught up in several problems associated with iCloud storage upgrades, and I hope that other users aren't experiencing the confusion I've had.

Earlier in August I received an email reminding me that my free storage was going to expire at the end of September, encouraging me to reduce my storage or purchase a plan.

Using the iCloud interface within System Preferences, on August 11th I upgraded my iCloud storage to the 20GB band.

Today I received another email warning me that I need to delete some files or purchase an upgrade before the end of September. I went into the iCloud interface again to check, and it was clear that my current storage plan is now the 20GB plan. It is not possible to select "Next" and purchase the plan, as it is indicating that I am already on it.

I rang up Apple Support who told me that I have not upgraded, it's just looks like I have, and that it isn't possible to upgrade my storage until two days before the 30th September.

What kind of online subscription service is so inflexible in terms of payment? And why is it so difficult to determine if I've upgraded or not? Why did it not work when I upgraded before?

I am confused and irritated and noone at Apple seemed bothered by what seems to be to be a complete mess.