Customer Claims I sent an Item my Store Do Not Sell

[Gamingpandà]

My business is relatively small, and I am the only employee. I do all of the ordering, shipping and customer service myself. I have a customer who claims that we sent him a product that we do not sell, that I am unfamiliar with. The product is larger in dimension than the package we sent out to him. I believe 100% that this is a scam. (Customer ordered bicycle grips, and claims he received a bicycle headlight conversion kit). What should I do?