Can i charge my billing in my postpaid monthly plan instead

Hello jessa35,

Thanks for asking about switching your payment method.

This article shows it may be possible, depending on your carrier: Availability of mobile phone billing as an Apple ID payment method - Apple Support

If possible, use this follow on article to change your payment method: "Find your country or region in the availability list below, then learn how to change your Apple ID payment method."

If not possible, please check the info here: "Learn which payment methods you can use if mobile phone billing isn't available for you."

You also mention issues backing up to iCloud. Please check the troubleshooting here: If you can't back up to iCloud or restore from iCloud backup failed - Apple Support

Thanks and have a wonderful day.