I found a solution as follow
1- if you will use sim internet please check first if your carrier supported by Apple cooperations or not
some counties not supported for LTE or 4G
if so please don’t use 4G LTE as it will make conflict on notifications and use 3G instead for internet and calls
try to reset your carrier APN setting from cellular option
2- in case of WiFi notifications not received it is a big issue from your internet provider
first download VPN application like VPN master from App Store
connect throw any another fast network, he will connect you automatic
it shall works well
3- Try to fix your WiFi to 5 ghz frequency and channel 11
you will find it under your WiFi router setting, advanced, WiFi, frequency and channel
it will give you fast internet speed and data and also prevent from toggle between 2.4 and 5
but take care as this frequency will affect signal strength throw walls
4- Update to last IOS version
5- Some people found a conflict throw iMessage and FaceTime
if you need to be sure just deactivate them as if as you can and see what will happened
Thanks and hope all be well