iOS 11.4.1 WiFi Calling not working

my mobile phone lg g flex  from korea ,wifi is not working .i have tried restarting and reconnecting a thousands of times but it doesnt work i have got it checked by a guy who is not very good at these things but he have the knowledge to solve this problem.i showed his but he said that it will stay like this.
it was working before but when i did factory reset in the mobile it doesent work the wifi .wifi network is connected but it doesnt works i have tried alots of other wifi connections but its the same i need it to work urgently and dont have any other device to use except for thiss laptop that someone let me borrow