Hi sally.madsen,
You're right, the payment information is not available in the Avast account, but you can check it using the details (order ID and password) from the confirmation email you received when you originally placed the order. I just re-sent it to you in case you no longer have it
About the price, you will receive an email with the details few days before the auto renewal, but as you mention the usual price is the one you see in the website