It might sound silly but are you sure you checked the right fuse? It's easy to be one-out, left or right or on the wrong row if it's a double-row fuse box.
Was the fuse the rating it said in the handbook - another pointer to having checked the wrong fuse. Have you put a meter across the fuse, not just looked at it.
Have you checked that other things on the same fuse are working?
Have you replaced the fuse anyway, just in case?
Have you got more than one 12v socket in the car?, so are you checking the fuse for the right one?
How do you know it's not working? Have you tried more than one accessory in the socket or put a voltmeter across it?