I can see all my notes.
I suppose this is some bug/glitch in the notifications received by Evernote from iTunes - to upgrade from Plus to Premium iTunes cancelled the Plus subscription and started new Premium subscription. If the notifications of these two actions were received in wrong order what might have happened is this - Evernote got notification that I paid for "Premium" and upgraded my subscription, but then it got the notification that my previous "Plus" subscription is cancelled so it cancelled my Premium subscription and this is why I am on "Basic" now.
Hopefully I will get my refund from iTunes, but now I am puzzled what would happen next and how can I pay for Premium without being downgraded again to Basic.
Here is the ticket number: #3195929
I have bad feelings for my decision to give more money to Evernote than I was paying so far (Plus subscription was half the price of Premium). Now I have semi-functional (basic) Evernote and I really need it on a daily basis on multiple devices.