If your fax number isn't showing in your Fax.Plus account, despite completing your payment, it's likely due to a timing conflict during your transition from the Free to a paid plan.
This rare situation occurs when the fax number you chose was secured by another customer just as you were finalizing your upgrade, causing your upgrade attempt to fail. However, if your payment went through, you can simply select a new number and upgrade your plan again at no extra cost. The payment you've already made will automatically apply to your new plan.