Samsung Galaxy S4 mini — My Samsung S4 mini cuts during a telephone call

I recently bought a samsung galaxy S4 Mini and its not even a month old and during calls it cuts and I can hear the person saying " hello hello" but when I try to reply they cannot hear me then it stops and switches off. All the other applications I use blue tooth, Facebook,whatsapp and viber work without any problems, even text messages.

Its just when I receive a call or I call someone it works for 1 min then neither person can hear the other.

Any advice as I am taking it for repair today.

Thank you.

Anne