@Barbiegrrrl have you made the purchase yet? Go to Payment & add-ons page click the Shop Add-ons button and then you can make the purchase there
Once you made the purchase, you can logoff from My Account first, then reboot your device and you can use the new data add-on
if you go back to My Account after , you should also see it there. Just in case you don't see it there, no worry. try to login My Account again using Incognito mode or a completely different browser (Edge/Firefox/Chrome) and it should show the add-on. The reason it might not show earlier was that you are checking the cached version of the page, not the most updated details from the server. Also, if you go to Payment history page, you should also see 2 lines there, one showing the payment, another showing the add-ons you purchased
