CTM Defective Product & Return Delay!

I recently bought a cabinet set for my bathroom and not within 6 months the mirror started to flake from behind. I brought it to the managers attention at CTM, I kept having to follow up as I would get no response from her and every time I called she was either not in or off sick. Its been almost going 2 months and the mirror has not been sorted out. I was told to send photos then I was asked if my bathroom has ventilation and to show them the window etc. Its a bathroom cabinet set, why am I been questioned about the ventilation of my bathroom now? When they wanted to sell me the unit they didn't enquire weather I have ventilation or not? Why is CTM looking for an excuse for a defective product. I was then told they going to pass a credit which I didn't want, I want the mirror replaced and I paid a contractor to fit the whole unit so I requested CTM to come through remove and install a new mirror at their cost, which is still not done till date! Why are they so quick to sell you a product and follow up on quotes but the after service is so terrible!