Thank you for reaching out. I can certainly understand your frustration with not being able to make phone calls with your AKG type-C headphones. I would recommend testing your headphones with another device to see if you also experience these symptoms. This will allow us to rule out whether the headphones or the phone are the device with the symptoms you are experiencing.
Are you trying to use your headphones for phone calls on the stock messaging app or through a video calling app?
Did the headphones come with your device, if no can you please provide me with the model number for the headphones to verify microphone compatibility with the headphones?