[Rolo]

Well, this sometimes work for tangible products, but since you said that you do not require the customer to return the product, then it might be harder than normal?

Let them know that you have not received the product back from the customer. Include any contact you had, with the customer or let them know if the customer has not contacted you.
Also send them a copy of the web page that displays your mailing address and return information/policy, so they can see that you have made it very clear for the customer to contact you and/or return products.

Some banks want to work with you, however most will just process any internet related chargeback their cardholders want - no matter how much proof you got. Sad but true!