I used to live in the United States and now in Saudi Arabia I am trying to buy a space in iCloud, but the Saudi bank card is not accepted

Did you follow the steps mentioned in this article to change the country your Apple ID is registered to?

Change your Apple ID country or region - Apple Support

You can also use Apple Gift Cards to pay for iCloud services:

What you can buy with your Apple Gift Card or Apple Account balance - Apple Support

Hey there,

To buy apps from the App Store, use Apple subscriptions like iCloud+, or buy other media from Apple, you need an Apple ID and a valid payment method. See what forms of payment are accepted in your country or region ☞ Payment methods that you can use with your Apple ID - Apple Support

if you check it and your payment method is supported and you still can’t purchase more iCloud storage , you need to update your payment method or add a new one. If you already verified that a payment method is available in your country or region and you're still having trouble, contact your financial institution.