Iphone 7

So both of my kids have an iphone 7...and within a week of each other they both started experiencing the same issue. When they call on facetime or a regular call they cannot hear anything and the caller can not hear them. Also i should note that the speakerphone option is grayed out as well...we have tried all the online tutorials for restarting, checking the charger port, and nothing seems to work. The other night my oldest couldn't text or do any communication at all for several hours as well and then it mysteriously started working again. Please help!