Issues with voice calls

I have an iphone 4. When i try to make a call, the phone automatically goes to loudspeaker. The person cannot hear what i am saying neither can i hear them. when i record voicenotes i can hear them very clearly. i even tried using headphones and a bluetooth headset, but i still cannot hear anyone when i make a call, neither can they hear me. I can make calls using viber and skype and it works perfect.

I even updated my phone and also restored it to 6.1.3

I really dont understand whats wrong with my phone.