To resolve this issue, support will need to check that there is an active MyPay account for the email address, and if so, have the ability to send a password reset. Please raise a new case online and reference the title of this article.
If you have NOT registered a MyPay account already:
From the MyPay login screen click Register Now (if on a phone) or Sign Up Now (if on a computer)
Fill in the form with Email Address, First Name, Last Name, enter a password and confirm the password
Click the "I have read and agree to the terms and conditions" check box
Click the Register button.
You will receive a confirmation email for your registration, and you should also then be able to log in to MyPay using the credentials you set up in the register screen.