Calls not connecting - iOS 8.4

I updated my iPhone 6 to iOS 8.4 a couple of days ago. Initially everything was fine but as of this evening I'm unable to make or receive calls.

If I try to call my husband his phone rings, and if he answers it appears to connect with the timers incrementing, but neither one of us can hear anything. If he tries to call me the "speakerphone" icon never enables, remaining greyed out. I noticed as well that if I go to Voice Memos app the record button remains constantly greyed out, and I cannot send voice commands to Siri. It's as if the mic has frozen but I can't find any settings to verify this. I can send and receive text messages.

I've tried:

- Power cycling the phone

- Hard Reset (pushing and holding the home + lock button)

The problem persists.

Anyone have any thoughts or ideas on what to try next?

Thanks