We can't see into your account. Are you sure you're on the right region? Different regions have different collections. There's also big changes coming in a few days with the Core Set, it might be that you're looking in the wrong places due to the changes, the cards still exist.

There seems to be a ton of bugs related to people's collection and Wild becoming locked. Try playing one game against Demon Hunter in Practice mode, that might fix it (it fixed other related bugs).

I’ve been playing daily since day one. Play wild as I use all sorts of cards and never seriously. 
They are all gold. With update 20.0, a bunch are gone. What happened? 
Sorry, I don’t know the right terminology. I just want my cards back.
Thank you!

Where Are My Cards??