can't log in

Long time ago I had this email let's say x@yahoo.com after some years i delete and made a new one x@gmail.com. On my PC every time I try to log in it goes like this: I put my x@gmail.com i put my password and it sends me a code on the same Gmail address... Very simple right? I put my verification code in and it says wrong password for email x@YAHOO.com... WHY DOES IT CHANGE MY EMAIL FROM GMAIL TO YAHOO ? I'M LOSING MY MIND I CAN'T LOG IN ON FRESH WINDOWS INSTALL!!!! I even reinstalled Mozilla, I've cleaned everything there is too be cleaned from the browser and same stupid "feature". Whyyyyyyyy????