As the email is asking you to log into your account on PayPal and not giving you a link within the email, then it could be genuine.
You have to register a credit card when you sign up for an eBay account and PayPal is part of eBay!! Anyway, you've done the right thing if your not happy with it, PayPal will answer the email and let you know.
I've had a number of spoof emails reportedly from PayPal asking me to log into my account using a link at the bottom of the message, not very well done cos if you "mouse over" the address another url appears at the bottom of the screen! Dead give away that it's spoof!!
Anyway, I've sent every one of these to PayPal and checked the site within 24hrs and each time it's been closed down! =D>
So it does help to send them in, don't just think "well they won't take any notice" cos they do.