Your requirement: Don't want to show the Page A again after the order has been placed.
Solution:
Please try location.replace() in JavaScript.
If you use location.replace("URL of page B") in the page A to open the page B, the URL of page A will not appear in the history list of the BACK button on the menubar of the browser, so user
can not return to the page A from the page B by click the BACK button.