Iphone 7 Plus heats up while using safari

iPhone 7 plus 128GB Version 11.1.1. Using safari or keeping the safari application open causes the phone to heat up and drain the battery. I have as advised by Apple technical support done a complete factory reset and set it up as a new phone and also updated the software through iTunes, but it has't helped. I am now forced to not use the safari app and use another browser which I downloaded.

Its been over a weeks time since apple senior technical support team is to revert to me.