Accounts being hacked

When attempting to login, I noticed I had my account password changed today without permission. Apon checking email, I received an email about Friday, March 30, 2019 7:05 PM Central Time, however I recorded nobody logging into, or accessing the email address on file to click the actual link, therefore, I don't understand WHY my password stopped working in the game client when I attempted to login. I had to reset my password at 8:05 or so PM Central Time to regain access to my account. Why did riot allow a password change without the link verification being clicked?

I need to know exactly what happened, what IP addresses were involved. Who can I go to to figure this out? I use a very long password, so it would not have been guessed.