Why is Lenovo K5 note turning on?

My phone is not turning on ,after the battery died, i charged it again it got charged till 67%, i turned it on, and was going to unlock it , it got heated up and turned off, i tried to turn it on again it didn’t and tried charging , it was not even charging , but the phone was still getting hotter and hotter , so i took it to a local phone repairer , he opened the phone up and remove the battery jack , and whenever the battery jack is connected back it is heating enormously ,please suggest me ways to find the problem and repair it.

i will really appreciate the help :(.