Poor service Pick 'n Pay Jean Crossing

I bought a Twisp at PnP Jean Crossing for nearly R1 000. I filled it and when trying to smoke it, it made hissing noises and like small explosions and also got very hot. I cleaned it and put fresh oil in and even tried the other filter, but same story. I was scared it would explode in my face. I took it back to exchanged but the floor manager told me he can't replace it because it was opened. I said to him would I know it's not working properly if not opened. So have I wasted my money or can I do something about it?