Why won't back button and some part of the screen work on the Lenovo A6000 Plus?

I brought Lenovo a6000 plus mobile six months ago in early months mobile was ok but now the back button and portion of screen is not working.
I did factory reset five times after that also the problem is not solved.
Can you give me any suggestions so that I can rectify it without going to service centre...

Hi sanjeev. Looks like you really need to visit a service center even just for a check up. I think the screen is damaged or have some lose connections in it. Have it checked.

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