Go to the Store
I would highly recommend going to the Apple Retail Store, where you purchased the bumper. I went round and round with Apple Customer Support and the Retail Store, and finally went in. All they had to do was verify that no refund had been processed, and then issued me a refund in cash (even though I paid with a debit card).
As an aside, I received a call from Apple Customer Care today. The gentleman who called told me I would need to go to an Apple Retail Store to obtain a refund. When I asked him why Apple's website stated that refunds had already been issued, and that I could check the status of the refund on Apple's website, he said he needed to, "verify that." I told him not to bother, since I had already received my refund. Long story short, I do not think the Apple Customer Service representatives have much of an idea of what is going on.