Troubleshooting:
Check the user account associated with the email sent from
Navigate to Users->All Users
Search for the user by email address
Click on the username to edit the user
Scroll down to the 'User Enrolled in Courses' section and check which courses are listed on the right
If the course is listed, check if the progress is complete. Reset their progress and respond to the user with the "Course marked as complete" Saved Reply.
If the access is not added, then search for another username by last name. It could be that they used a different email address when purchasing with Paypal.
If a different email address was found that seems to match the user, check the access and if the access is added, email the user and let them know, that the access was added to the Paypal email address. It can also be added to the main username if requested.
If the username cannot be found, ask the user for their Order Number. Its possible that they used another email.