wifi calling issue s6 G920A

I am currently using samsung s6 G920A in pakistan my phone does not support wifi calling but still whenever i recieve call or make call it gives an error that all cannot be connected over wifi . But there is no option to disable wifi calling as in my country we dont have wifi calling .. before that i used to call and recieve calls normaly i m facing this issue since 2017 dec.i can make call nd recieve call but it cannot connect . What to do now ?