As for using revolut, refer to Payment methods that you can use with your Apple Account - Apple Support
To what kind of email account are you referring? iCloud? If iCloud is refusing to store email because your iCloud storage is full then you need to permanently delete items or subscribe to a higher storage level. Note that deleted items in iCloud are often retained for 30 days and will continue to take up space until they are then automatically deleted. You would need to permanently delete them to immediately free up space. Different features may have this, but here is the one in Photos:
Delete photos on your iPhone or iPad - Apple Support which notes, "If you want to permanently delete your photos or videos, you can remove them from the Recently Deleted album. When you delete a photo from this album, you can't get it back."
"Permanently" means "permanently", with no chance of recovery.