Hi,
Any chance it's a LOGITECH?
I solved this problem by jamming a thin piece of material (plastic/foil package folded over) under the left mouse button and pulling it to the rear of my Logitech G400S.
I managed to get rid of the double-click, then cut it so only a little stuck out.
Finally, I removed it after several weeks and I guess it WARPED the plastic enough as it no longer double-clicks.
(So in my case the main top of the mouse is hitting something beneath before the click happens so you get a double-click feel and sound. By warping the way it sits i avoid the first click. It's a problem with several of the Logitech models.)