Musescore.com pro account issues

I have tried twice now to upgrade to a pro account on Musescore.com and it has not worked both times. The first time it said my payment had been refused. The second time I tried it with a different card and was redirected to my "issuer", which then pulled up a blank page. I don't have any other cards I can try, so I'm wondering if there's something simple I'm missing.