NHTSA Complaint #11495961 — 2009 MERCURY MARINER

While driving vehicle brakes all of sudden go to the floor, no pedal response. This has happened a couple of times without warning. Once when I was approaching an intersection and light changed. My brakes all of the sudden went to the floor and I had to downshift and cut my wheels toward the curb to stop from crashing. Then a couple days later attempting to get it to mechanic it was fine and pumped properly. I wrote it off as a fluke. Then a few months later it happened again. My mechanic can't seem to find the issue and has charged me for new brakes, new master cylinder, new brake line, and another part for the abs power assistant. My car still continues to have this brake malfunction on and off. Somebody is going to end up getting hurt. This obviously is some kind of part defect. Please help!