I recently purchased a Pulse Oximeter Lk88 on eBay.  After it was delivered it worked satisfactorily about five times but after that the LED display didn't show anything but coloured horizontal lines. I want to return it but when I enter the order number into the search box it tells me there are no order can be found in the system, and apparently there is no other way of making a return.  What can I do? A.G.