based upon what I'm reading and seeing, I think someone sold you poorly refurbished fans as new.
This may not be the direct fault of the reseller either, it could have been a supplier that ripped off a reseller, it happens on Amazon all the time.
yeah, looks like they've used old motors on new blades and bodies. Even cloned Deltas wouldn't die that fast. When you say 'dead' are they just not turning anymore, or locked solid/hard to turn by hand?