Yes, of course I read his post, but there was no indication whether he was trying to do this in the correct way as I listed above or using the normal upgrade process, which apparently doesn't work - or indeed whether he is trying to maintain his storage level or change it. The process I quote is the correct one but not everyone has been following it (it is hardly intuitive).
When you follow steps 1-5, do you see what is in the screenshot I posted, or something else? Does it give the expiry date as shown in the image? Are you trying to maintain the storage level you currently have for free?
The process shown above has worked for most people, so either there is something different about your situation which is affecting it (for example if you bought any additional storage in the last year) or there is a technical issue which only Support can sort out. It the latter, go to https://expresslane.apple.com ; select 'iTunes', and then 'iTunes Store'.