All connections dropping down after a while
I had this kind of troubles before(not screen flicker). 

You could try to factory reset and make fresh clean install of stock firmware. 
Edit: Remember to backup your data. 

If you are using some custom rom flash it after doing stock and make sure to check from xda if anyone is experiencing similar issues. 

Issue could be related to some sort of corruption which could happen if flashing went wrong or tweaking while rooted. 

Normally when flashing orginal stock firmware this fixes issue. 

You could also try to check SIM card(take off put back) and take battery off for few minutes(this preforms soft reset and sometimes could fix some problems). 

This brand is not familiar to me but i hope this helps to your problem.