What else do I have to say?
I'd like to get the subscription done, but honestly, I can't.
Credit Cards are only a thing in the USA, I mean sure, here in Europe we also have CC but we don't use them.
If you really want to give everyone the option to actually get a subscription done, then you have to include more payment options than something that is almost a region-specific one.
Please consider adding Paypal, it will help you out because so much more people will be able to upgrade.