While it is a fairly rare occurrence, for stubborn clogs you may need to use more than one CO2 cartridge. The SurePlunge automatic toilet plunger is extremely effective, even with very stubborn blockages.  But if after using the SurePlunge several times and the blockage is still apparent, the most likely the problem blockage with a “foreign object” … something too large that it cannot pass through the toilet “S” bend. If you have an object that is too large to pass through the toilet “S” bend, it will have to be “snaked” back outwards.  It will not pass through the bends. Also, while rare, but possible, you may have a physical damage elsewhere that lies within the piping fixture or outside drain and no amount of plunging will resolve the issue.