Hey there Alina....
Yes, our coalition did achieve Heroes of Ecumene many months ago. It was sometime around last November to this January time I believe when we obtained this, when I placed 3rd for the "siege" weekly rankings. I am sure you must have some record available that tracks those old rankings?
I did not take any photos as it correctly appeared on our coalition information page, and we received the rewards. The only evidence I have now I guess is the screenshot below showing that I achieved the personal achievement Heracles for ranking in the top 10 in the past. Since I have never left my current coalition, obviously we should have it valid for Heroes of Ecumene Level 1 still.
If you can look into this, that would be great. Cheers.