In that case, you know they are lying. If you used a flat rate box, then it got shipped successfully. They did NOT get charged any COD.
This is where you just decide what you want to do. You are 100% in your rights to say that they bought it, paid for it, and received it. You don't have to give them a penny if you don't want to refund them. If they want the money, they can sell it to someone else.
If you do feel like being nice and letting him return the tablet (and that is the case. It would be you doing them a favor, you are under NO obligation), then allow them to pay to ship it back, and you refund the purchase price, but NOT the shipping price. You will be able to sell the tablet for the sale price again, but you're not going to be able to make up your lost shipping costs, and this is clearly no fault of your own, so there is no reason you have to suffer at all.
no subject
This is where you just decide what you want to do. You are 100% in your rights to say that they bought it, paid for it, and received it. You don't have to give them a penny if you don't want to refund them. If they want the money, they can sell it to someone else.
If you do feel like being nice and letting him return the tablet (and that is the case. It would be you doing them a favor, you are under NO obligation), then allow them to pay to ship it back, and you refund the purchase price, but NOT the shipping price. You will be able to sell the tablet for the sale price again, but you're not going to be able to make up your lost shipping costs, and this is clearly no fault of your own, so there is no reason you have to suffer at all.