I saw this post in Russian, and I didn't know they gave away mystery boxes on PoE, since I don't really go into buying much from the shop, but if you go to your MTX stash, there should be a Thaumaturgy Mystery Box waiting for you.
Your account have to be older than a day, I suppose. But if this post was already made, then my bad. I just saw it in Russian and didn't find any in English. Good Luck!