general problems of the 2006 Mitsubishi Eclipse

I was making a right to enter a church and as I was slowing down I lost complete pressure of the brakes. I have taken it to two mechanic but the problem goes away after a day. They told me the brakes were fine. (one of those being a Mitsubishi dealer). This was very dangerous because if there was a car coming out of the church I would've had an accident or crash.

I was driving the car normally fine and there was a small pot hole on the ground that I went over. I had my foot on the brakes while running over the pot hole and the pressure on the brakes were completely lost. It was a spongy feeling as the brakes were to the floor. The brakes had very little power and when let go had a whistling sound coming back up. I had to drive home while down shifting to lower gears because the brakes did not work.