brakes keep giving out, peddle goes to floor, put in park

I have had the brakes 2 x, the line, the master cylinder redone, and still this problem persists. I do not trust this vehicle and am scared to drive because of the pedal going in. If I sit at a light on the brake pedal, it will go in and I have to put it in park, pump the brake to get the pedal tight again and to take off the brake light. What is going on....this is like an accident waiting to happen. There should have been a recall for this vehicle!!! If there has been, I have not got it and I bought this vehicle from the original owner and I have all his mechanical work and mine. Can somebody help??