Can't Log Into Facebook

I changed my FB password (successfully) yesterday. When I tried to log back in (both on my PC & my phone), A Whatsapp("WA") window appeared. It wanted a code sent to my phone to log into FB. Checked phone - no code. Now I can't get into FB without that code. Looked up info on the web & it says I likely changed it to "WA" as the 2nd party authentication method (no, I did not! I always get a text message, messenger, and a notice from FB).
I don't have anything linked to "WA", nor do I even have the app downloaded into my phone or PC. The web people all say to make changes (IN FB): "...go into your FB account, and...." - well, I CAN'T GET INTO MY ACCOUNT, so how am I supposed to change it? Can anyone out there please help me? Please and Thank you.