You can request a check for the credit balance to be sent to you - it can be done online. Dont know under which tab this feature is hidden now with the new design. However, the function is there. Incidentally, Citi also now allow you dispute charges online - a new feature.

Check takes a week to 10 days to arrive. In the interim you would see the credit is offset by the check on the unbilled activity screen.

Dont cancel your card until you receive the check as you never know if it could be lost in mail. A dividend card rebate check was lost in mail on my account about a year ago, and it took another month to get the new check sent and be received.