Skoda Brakes don't work at stop and go traffic?

My Skoda Octavia Petrol RS model sometimes does not stop with brake pedal not pushing down when pressed during heavy stop and go traffic situations. I have taken this to garage several times during last 1.5 years since I bought the car. Any advice on diagnosis/solution?|||your question is sort of vague, but ill try my best. if the pedal feels spongy then there is water in your hydrolic system, drain it and refill. if the brakes just completely go out sometimes, then it is definatley the booster or master cylinder (or a vacuum line connecting to the booster) have the parts tested and/or flushed. good luck