I agree with alleyoop1. I would take it back and see if you can make it fail while there. (Of course it probably won't!). If nothing else have them watch while you thread it and verify the thread path.
How/what are you sewing when the breakage occurs? Just piecing? FMQ? Embroidering?
Another thing you might want to try before that: lowering the thread tension a bit. Skipped stitches is often a needle problem, as is shredding so I can see why they suggested the needle changes, but sounds like there's something else too.
Last edited by PaperPrincess; 01-22-2015 at 06:34 AM.