Chief Aircraft Changed terms of sale after completion, refused to refund core item after it was returned. Grants Pass Oregon

I ordered a Bendix Magneto from them. I called to confirm the terms and core policy. I was told on multiple occasions that as long as I returned a like core that was NOT a Sigma-tek or Tempest core it would be fine. I got the UPS tracking info called an Airframe and Powerplant mechanic to come to the airport to install the replacement mag. When he arrived and opened the box there were different terms inside the box! I had already paid the A&P for the travel time, so we had no choice but to install the mag. I didn't think it would be a bid deal as the removed mag worked until the internal gear shed a tooth on takeoff!
So I try to return the core and they refused to refund the core charge! They then went on to say that they will only fully core refund working parts! Why would you change the part if it was working! This is false advertisement at best more like down right theft! They lied, didn't honor the original quote, and ultimately charged me almost 40% more than the quoted price.

I have the original quote that says nothing of these new terms.