No feedback and refusal to return calls

I have a Renault Megan that came standard with a TomTom - the TomTom kit is not working and has been giving problems from day one - it is the memory card that is the problem. No one at Renault Tokai will help me - they want us to take the car in again and again and still the same answer - they can't help me! or they won't help me - empty promises - what does one have to do to get this issue sorted out. I phone and each time get handed an empty promise someone will phone me back - still waiting! The staff at Renault Tokai should all be fired!