No need to apologize for asking questions
They would tell you to change it every two weeks if they thought they could get away with it. They want you to change the filter media so that you buy more filter media. It need not be changed until it's falling apart. The carbon inside will become useless (has long since been useless) and just becomes more room for the bacteria to live on. Many people do not use carbon in their tanks - that's literally the only reason why you "should" change the filter media. But as I said, your tank will be fine without it. It's been fine without it. The amount of carbon in a filter cartridge is pretty small - it becomes used up well before the month is up.