Apple ID not valid

Hi,

I have forgotten the password for my apple ID (xyz@gmail.com). when I use the 'iforgot' website to reset the password, it says the xyz@gmail.com is not an apple ID. I put in my first name, last name and the gmail account to find the apple ID and it pulls out xyz@gmail.com as the valid apple ID. I try again with the same xyz@gmail.com apple ID to reset password, it again says it's not an apple ID. I am stuck!