After 3 months only limited use

In the beginning you could use the pan normal
During the first weeks a brown discoloration from center began (the color itself does not bother me)
At this brown discoloration sticks each product immediately fixed (it burns on tight)
After 4 months now, the bottom surface is colored brown to about 50% and everything is burning there now fixed
Have this now claimed as material defect the dealer
Answers from merchant:
1. Answer: This is a natural discoloration, no shortage
2. Answer: Quote from email: "The color changes in the ceramic pan are residues of food, which they have previously prepared in the pan These have been at that time not completely removed during cleaning, so that they are at the other uses of the pan. have burned or discolored "
The pan was like all my other ceramic pans (which I already have several years) washed by hand
Here an attempt is made to give the customer the blame for a defect
Now I can only say shame shame, shame shame, ....