Cannot upgrade iCloud
Hi. I am out of storage on the 200GB plan and have been trying to upgrade to the 2TB. When I go through the steps, it sometimes comes up with a box saying I am already an Apple Music member, and then I do not get any further before it returns me to details of the 200GB plan. I have tried it on my iMac and my iPhone. On the iPhone I have tried signing out and in again of the Media & Purchases. I have macOS 13.6.1, which should be sufficient according to what I read. My username and password are correct. I have no further ideas, but it is getting pretty annoying as I have stuff that is not getting backed up onto cloud storage, and despite being happy to purchase the upgrade, it seems I am stuck. Any advice welcome.
iMac 21.5″, OS X 10.10