Mobile Data blocked while getting/sending phone call and message
This all depend on your network provider. And also android operating system.
Generally in 2G network  when you get call, mobile data turn off. while in 3g you can use call and data simultaneously. This also depend on network strength and hardware.
while in 4G LTE, you can connect internet and make call.
So choose network which support data + voice.
kindly provide what is written near your network signal strength at the top of the screen E or 4G Volte.