Asha 30/40 Series :: Asha 302 Audio Recording Distorted After Making

I purchased Asha 302 about 20 days ago and while going through the features when I recorded some voice using voice recorded output was distorted, I contacted Nokia support through email and was told to restore factory setting. After doing the same I recorded and played AMR file it was fine but as soon as I received a call and then I checked the same recorded AMR file it was againt distorted. I reported same to Nokia support and was told to contact Nokia Care Centre which I visited yesterday there NCC people re-installed the software/OS but the problem persists. I was told that phone has to be sent back to company. I am having another Nokia C2 phone which is fine and no such problem there in that model.