Digital currency is a generic phrase like God. You must prove that digital currency actually exists. But of course, we know that this is impossible.
So are you saying that anything digital does not exist or are you saying that nothing digital can be used as a payment in transactions?
I have this beautiful picture I just made in Paint with my computer. I saved it in cloud service Dropbox. Does that picture I can see in my computer screen exist or is it only my imagination?
To say that Bitcoin is digital you would first have to prove it exists. Like applications, ebooks, documents, animations, pictures, and other digital products exist. There's an enormous amount of digital products out there. Bitcoin is nowhere to be found. So when you say it's digital you're imagining things.