Poor focus above 12 power - Burris Fullfield E1 4.5-14x42mm 1in Tube Second Focal Plane (SFP) Rifle Scope

I’ve been shooting for over 50 years. I have had Burris scopes on rifles as well as hunting handguns. I always admired their quality. I purchased this scope and discovered that it’s blurry and out of focus between 12 and 14 power. I sent the scope back and they returned the scope with a note stating it was fine. The tech said he tested it. I’ve had several friends look through the scope and they all stated that the quality of the image falls off between 12-14 power. Now what do I do? Only use on lower power settings? I’m very disappointed. I replaced this scope with a different one from another manufacture. Now this just sets in a box on my reloading table. So much for no questions asked warranty.