See if Apple support's online article (link below) can help:
(Scroll down to see pricing / plans available / for your country or region)
iCloud+ plans and pricing - Apple Support
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If you do not already have one listed:
You may need to add a payment method to your Apple ID account for the monthly payments:
See what payment methods Apple can accept in your country or region:
Payment methods that you can use with your Apple ID - Apple Support
How to Add an Apple ID Payment method:
Add a payment method to your Apple ID - Apple Support
NB: You may need to allow 24 hours for any changes to come into effect everywhere you use them.
Apple support have a video online (see below) that may help you :
All the best :-)
https://www.youtube.com/watch?v=RcqL6JqyJQQ