Mixet Cartridge Leaking

My shower is leaking from the spout is a single handle mixet brand. I replaced the cartridge and within a couple of days it is leaking again and pretty bad. I have done this twice with the same results. I also have replaced the handle to make sure that was not the problem. The only odd occurrence is when I was doing the initial replacement the water was inadvertently turned back on and water shot out of the pipe. Any ideas?