If you had submitted your amended tax return electronically via NETFILE, there is a CRA NETFILE confirmation number you will see in the return that will confirm your successful submission to the CRA. In order to check this, log back into your 2018 account and select the return that you chose to ReFILE. In the navigation bar on the left hand side of the window (as shown in the attached screenshot), select the 'CRA Online Mail' and on that page, click on continue. You should see the page with the CRA NETFILE confirmation number if you have submitted your ReFILE return successfully.