In my account I can see 6 other databases, but not that particular one.
I cannot find any email about the firebase db.
Also, As much I remember I didn’t touched firebase console recently.
The problem was…
I was deleting some unnecessary projects at Google Developer Console.https://console.developers.google.com/ (not at firebase console).
And I deleted this project by mistake.
Anyway, I got my database back. Firebase support was very helpful.
It is now ok.
Nope… I didn’t delete the database. I deleted the project, outside of firebase console; through Google Developers Console.
So, the lesson is: We should handle Google Developers Console with care.