I think the problem is not with the phone, but with the cellular network, which could be missing. There are times when the connection is broken and the call goes with it, especially when you are standing in traffic. Try to change your phone number to another, for example, I use VoIP from
https://www.mightycall.com/toll-free-number/ because it is more secure due to connection to the Internet, which means that no one can listen to me.
