Test it with another lens first before sending it off.
Seems really odd you could see any BF really. At 65mm the lens should be at almost f5.6 and your depth of field should be about 3-4 inches shooting at a subject at 5 feet away.
If it were me, I would set it up on a tripod, put a beer or pop bottle on a stool at a measured 5 feet away (from the hot shoe mount), set the body to "S" AF and single spot, focus on the cap, and use the timer to fire the shutter, and see what happens. If it is blurry I would add two more bottles stacked behind at a 45degree from the first one to see it it is back focusing. Still not working, stack two more with an aspirin bottle on top of the last bottle - either way you will need that for later.