No Refund due to the Box

We ordered a second hand monitor, order#:***, and when we received it, we found it not to be compatible with our laptops. We decided to return it and ask for refund, which we will then top-up and purchase a more compatible one FROM THEM. They returned the monitor back to us saying thats not the box they received it in. On the day we opened the box, it was a bin day and we threw the box away. When we returned it, i was well packaged in a box and the drivers picked it up. Now they are refusing to refund us because of the box. Really?