Help mE PLZ!

ok I have a serious problem. Everytime I slow down or stop the car, my engines turn off itselfs. Its like its stalling on me. I have to pull the ebrake and shift into park to take the key out and restart the engine. Took it to my dealer told them the problem. They said they checkd the engine and no codes came up. They drove it and tried to make it stall but it wont work. So I said ok and took the car home. As I was driving home, damn engine stalled on me again. I noticed the the key on the panel was flashing. I took it back and told them the key was flashing. They told me it might be a communication problem. But I thought i asked here also because u guys are very helpful. Anyone know what is happening? Im scared dealer will call back and tell me "cant find the problem". Thanks in advance.!