Brake Pedal And Linkage problems of the 2005 Nissan Sentra

I own a 2005 Nissan Sentra, bought brand new from the dealer. I maintain the car like a baby. Two weeks ago I had their 100 point check up, brakes checked, wheel alignment and all. On my way home from this service checkup, the back breaks started making a thumping noise, I went back to the dealer yesterday, waited there for two hours for them to "fix" the noise. On my way home on this rainy day, my car skidded out of control, when I tried to slow down as I was going onto an exit. The brakes absolutely did not work and the car bumped the curb at least 4 times before it finally stopped. I tried applying the brakes while the car was going insane, but it didn't help. This is not the first time that the brakes failed on a rainy day. The other time it happened I was actually inching in traffic, the car stopped short an inch from the car in front of me, and only because that car moved forward. Apparently these brakes aren't made to work in the rain.