Pairing request pop-ups from other wireless keyboards

I work in a place where there are at least 60 iMacs in close proximity. From time to time, I am certain that some keyboards have got muddled up.

Mine is probably one of them, because my wireless keyboard is paired fine, but another keyboard keeps sending a pairing request constantly. (By constantly, I mean a few times per minute) for the last few months. It pops up in front of my work, making my time less productive as I have to constantly reject this pop up in order to carry on working.
I am not sure how to stop any other incoming requests besides my own keyboard and mouse, nor am I sure of how to find this phantom keyboard.
I have attached a screen shot

Thanks for your help

I have indeed tried that, yes. No changes.
I have also tried deleting the bluetooth plist, which did nothing for this issue.