Brake Disc Pads problems of the 2016 Mazda CX9

Both rear brakes locked up on separate occasion while driving on the freeway at about 70 mph. Each time the brake engaged themselves and locked onto the disk/rotor. This caused the pads to burn up and produce a larger quantity of smoke. On one occasion the rotor became red hot, flame was visible, lots of smoke was being produced, and it warped rotor. Every time it occurred I stopped the vehicle and turned it off. After the restart of the vehicle the brakes were not locked but the vehicle would shake as now the rotors were warped an the pads were destroyed. I took my vehicle to the Mazda dealership and they informed me that I needed new pads, I did but it was due to the rear brakes locking up on their own. I got the pads replaced and 6 months later it happened again. This time I recorded a video on my phone and showed the dealer ship what I experienced again. This time they informed that I needed, new brake pads(again), rotors, and piston but they did not address what is causing the rear brakes only to lock up on their own creating excessive wear and damage to the brake components. Something is and continues to engage my rear brakes. It last occurred on 10-04-19 and it has only been 3 days since the Mazda dealer replaced the damaged parts and under hard braking the vehicle continues to shake which are early signs of what happened before, so its only a matter of time before it occurs again.