No afterservice

I recently wrote a review about the bad service from TATA, I purchased a Mitshibishi through them in April was told the car had just been through a service. I also paid R6000 which was included in the price of the vehicle for a service plan. Now wanting to take my car for a service I was told by Mitsibishi that I had already missed two services and I would have to pay for a service out of my pocket. Also the warranty would also now not be valid. I received a response from them saying they would get back to me but I have heard nothing. You cannot get hold of anybody telephonically, their call centre does not even answer the phone. What do I need to do to get some service.