Hello ThienDuong ,
did you manage to get your files yet? The format of the file you downloaded should have been ".zip", when I download them I get "microsoftcertificate.zip" out of it. Try that.
Otherwise I can only guess that you might have JavaScript or some Cookies of the relevant pages blocked. Perhaps try if you can open the page for the certificates directly, at https://mcptnc.microsoft.com/certificate. I have had issues with the pages regarding blocked "third-party cookies", since Microsoft is using a number of different pages that set cookies, i.e. login.microsoft.com, login.microsoftonline.com, login.live.com, login.windows.net, examregistrationapiappservice.trafficmanager.net, etc. These blocked cookies turned out to block me from accessing the PearsonVUE webpage and others in the past. When I use the webpage, I get quite some redirects which may break the access.
Kind regards
Jan