Shooting wrote in post #17920647
Ok. I always have the middle one and it is always back focusing when the people are 15+ feet away and I'm at 24mm. It worked 3 months ago when I got it back and now back to not working again.
So you are saying that maybe I should choose another focus point? Live view should work because it is spot focus, supposed to focus on whatever is in the focusing square, I do magnify up to 10 and it gives a green square when focused but it doesn't come out focused, live view is no help. Neither is zooming in, focusing and zooming out.
I have tried focusing on a face in the first row with one row behind them and yet it is the wall behind both walls that are in focus, I even moved the point down and focusing on a shirt with what I would consider a high contrast design and yet still it is the wall behind both rows of people that is in focus. If it is a single person I would try to focus on different things and yet it is what is behind them that is in focus. I'm at my wits end with this lens.
If you are LV focusing at zoom 10, and you SEE that the image is sharp on the camera's LCD, but when you take the pic it isn't, then either:
A: focus changed before you tripped the shutter (are you immediately tripping the shutter on green box?)
B: the point you focused on was the only 'plane of focus' that's in-focus, and the rest of the subject is out of that plane (but this doesn't match your descr. of the wall behind being in-focus)
OTOH, if you are saying, above, that LV -with green square (indicating AF successful)- is NOT achieving focus, then flip the AF switch on the lens to 'ON'... 
But seriously, I cannot imagine LV showing green if it didn't achieve focus. Send in the lens and camera.
Watch the lens' distance scale when you AF. Do you see it moving?