You might need to perform a "gulp"...firmware update to your receivers - I had to do this a few times for product that I had purchased from various suppliers. Its super annoying that there is so much inventory of those things floating around with old firmware loaded - I was ready to throw the thing at the wall before I calmed down and started digging.....sure enough I found the primary reason they wouldn't bind was firmware mis-match.
Its kinda the devil in the details for them being so inexpensive....
There's a handful of video's on youtube outlining the process. I've attached a link for reference/..