I have changed to a new number now and trying to enable my keychain but it keep sending the code to my old number. Other option that shows is to contact apple support. How do you do that?

i have just lost my number that i use to sign up for my apple account few years ago and now i am using a new number. I am trying to activate the keychain but its sending the validation code to the old number instead of my new number. Ive try everything to put my number in to the apple but the old number remains the primary. How can i change that? The other option that i was given was to contact apple support to validate my account but i dont know how to do that. Any idea would be appreciated please