how do I pay my iCloud bill

iCloud storage subscriptions are automatically billed to your payment assigned to your AppleID. If you have a balance of funds associated with your AppleID, the fee will de deducted from that balance.

iCloud storage plans and pricing - Apple Support -> “Accepted payment methods for iCloud storage upgrades include credit cards, debit cards, and your Apple ID balance. If you don't have enough available funds in your Apple ID balance to complete your upgrade, you'll be charged the remaining amount. Apple Store gift cards aren't accepted as payment for upgrading iCloud storage. Learn how to manage the amount of storage you're using.”

This is not a chat line.... this is a USER to USER forum. You are not addressing Apple here. If you need Apple Support about billing related to your account, click CONTACT SUPPORT in the top right of the page.