Have you tried to email them yet? They may be legit.
Ebay rules for canceling
Examples of legitimate bid cancellations:
The bidder contacts you to back out of the auction.
You are unable to verify the bidder's identity, after trying all reasonable means of contact.
You want to end your listing early because your item is no longer available for sale. In this case you must cancel all bids on your listing before ending it.
If you feel you need to cancel it, go to site map and you will see "cancel bids"