Mic is not working when I plug in the earpiece

Hi all,
I am having Sony Xperia S Tablet and I have been using it since the last one year. Everything is fine so far. I never tried to use ear piece for Skype.
Today when I plug in the earphone, the internal mic got disabled and the receiver can't hear what I am saying. I have shown it to the Sony device center and they said the problem with the ear piece itself and hence I bought a new earpiece but with that one also the problem still persists. Hence, I feel that this is a hardware issue with tablet. There is no warranty for my tablet.
Any suggestions what I have to do in order to rectify the problem?
