HELP: Unable to return defective note (box missing) topic

I bought an open box note 10.1 a month ago but it turned out to be defective (screen frequently unresponsive on wake up) . I tried to return it but they told me they need the box because it has the serial number. I lost the box but the serial is already stored on the device. My question is:1- Do they have the right to refuse returning the device for not having a box 2- What should I do in this situation?

P.S I have one year warranty.