An order is never cancelled by a buyer until YOU agree to accept that cancellation. The buyer did not force you to cancel; you CHOSE to accept his refund request.
If an order is marked as complete, then you’ve done the work. You should get paid for that work. Cancelling an order just because a buyer says he wants his money back, sets a bad precedence, and tells that buyer, and others, that they can take advantage of you. They’ll know that they can hire you, have you do work for them, and then just demand their money back after delivery so that they get your work for free.
NEVER work for free. It surprises me how many sellers still keep doing this. You did the work, you should get paid for it. End of story.