I once had a similar thing happen when I had a credit card compromised. Instead of issuing a new card number, the bank chose to mark the card as closed, and reopen a "new" account for me. In my case, the only piece of my score affected was the average age of my accounts. I tried to get them to fix this by somehow marking those two accounts as one, but they would not.
In your case, I suspect the drop in your score is because closing that card changed your utilization ratio by reducing your total available credit. There are two quick ways to fix this:
Call the issuer of the cancelled card and see if instead of cancelling, they can reissue you another card. They may just open you another account like in my anecdote above, either way you can probably avoid a hard pull by going through them.
Open another credit card to raise your available credit and lower you utilization ratio. You'll have to take the hit of the hard pull unless you have an existing relationship with another credit provider.
As always, there are many helpful tools that can help you decide which actions to take by simulating the affect they would have on your score. cough.. credit karma