I have a Gessi oxygene wall mounted tap and it leaks when it is turned on weather it's hot or cold water.I'm having trouble getting the ceramic cartridge out to check if it's damaged.I've taken the head of to reveal the cartridge but I'm not sure if I have to just pull or undo the cartridge.The instruction sheet which came with the tap(6 years ago)says there is a tool to help with the removal but I've never seen this.
Any help or info would be greatly received.

Thanks,

RB