Ipad rear camera doesn't work

i bought ipad air2 1month before and rarely use rear camera

but one day when i use facetime and skype, i found that rear camera didn't work! only front camera did work.

i dont know why it happened, i installed normal apps in my ipad same as my iphone apps.

i already did everything as apple staff said, all setting resets, backup, sleep+Home button restart diagnosis checking and internet help center.

sometimes i found same problem in the Q&A board, nobody solve it

please solve this problem!! Please!!!