Cannot upgrade icloud 'something went wrong'

Whenever I try to upgrade to iCloud+ with my iPhone or iPad, I get the following message: 'Something went wrong. There was a problem upgrading your iCloud+ Plan. Try again later.' I have been trying again later for months now.

I have tried:

• Restarting my devices.
• Logging out and logging in with my apple account.
• Checked if I have added a payment method, I did.
• Checked Apple System Status, no problems.
• The network connection is stable.
• I also tried logging out at Media & Purchases and logging in again, a suggestion on macrumors.
• I've tried on my Macbook as well. This one does not give me an error message, it just doesn't give me the storage.

Can anyone please help?