Apm 2.8 mega lost accelerometer calibration

Hi, my apm 2.8 mega lost accelerometer calibration. It was crashed in flight once I tried auto pilot mode it flew like rocket around 20 feet then luckily one of its propeller fell down. After this every time I connect it to PC using usb cable to Mission planner it shows not level to ground. After doing calibration it worked until next time connect to usb or battery. How can I fix this?