Can't make a call out or receive any calls...checked everything

Can't make a call our or receive any calls...checked everything from sim card slot to call settings; powered off and on and even powered in safe mode. Tried different sim cards from different providers, nothing. Reset it to factory settings, nothing....had 2 more brand new BV6800 also same problem. Can connect to internet, texted and receive text but cannot do the one thing it was made for, make phone calls. It is frustrating because it could be hardware fault.