If you are unable to login:
If your payment wasn't processed completely, you won't be able to log-in. Check to see if you received a receipt from PayPal for confirmation of payment and a welcome email from ABC with your username and password.
If you didn't receive either of those emails then your payment was not completed and you will need to go through the sign-up and pay process again. (Note you will need to choose a new username and password)