Had my car for years now when I first got it tried connecting Bluetooth to IPhone 4, I could hear people talking but they couldn't hear me, tried a few times but gave up.
Sitting in car awaiting the return of the misses and tried my IPhone 7 paired and called my son it was perfect so am a happy chappie

PANDA 

Supporting the London Air Ambulance with my Brothers

Probably microphone wire is cracked, straight forward to replace if problem comes back.  Bodsys Brake Bible
Software Updates Contact me
RRS Timed Heat/Remote kits - Contact me
BAS Engine Re-maps/ EGR Blank EuIII and EuIV
Clock On The Dash/ SNOTM /3Flash / BT Update /Service Reset/Error Codes read\ Gearbox Reset
See it HERE

Thank's Bodsy
Where is it in the mirror??

PANDA 

Supporting the London Air Ambulance with my Brothers

The microphone is in the light unit, behind where you see those small vents above. The crack int eh wiring is usually before the connector. You can wire in a new wire between the radio and the microphone. Just need to feed it through and up the A pillar and along the headlining.  Bodsys Brake Bible
Software Updates Contact me
RRS Timed Heat/Remote kits - Contact me
BAS Engine Re-maps/ EGR Blank EuIII and EuIV
Clock On The Dash/ SNOTM /3Flash / BT Update /Service Reset/Error Codes read\ Gearbox Reset
See it HERE

Much appreciated  

Supporting the London Air Ambulance with my Brothers