maintenance plan

I bought my vehicle last year. I took it for saervice twice already. On the second service brakes were replace. About a month later they started making a sound so I took the vehicle back and it was repaired. About two months down the line my vehicle had a brake problem again and I was told by renault that the maintaince plan that I had taken when buying the vehicle has refused to pay because I recently changed my brakes. I am very unhappy because there is no documents that stipulate how long I must wait before my brakes are changed again.