Hello @ChrisK231 ,
The monthly invoices are there to reflect how much your costs are per month. You can view these individually in the My Account page's Billing Activities / Statements. You can also email or print / download these statements and invoices for any records you need to keep. You can also see your account's current balance on the My Account page. If it is positive, it will be just simple numbers, and if it's negative it'll be (bold and in parentheses).
We provide the monthly invoices so you can also keep track of how much is being taken out your pool. That way you can see if the price changes, and what the causes for that change might be - e.g. higher or lower contact tier, switched to the other plan, added another service like Inbox Preview or SEO, etc.