"We call them and they change it."
Translation:Vi ringer til dem og de ændrer det.
It isn't. Whether "den" or "det" should be used would depend on the grammatical gender of whatever the pronoun is referring to. For instance, you may have an appointment ("en aftale") with someone, and you might want to cell them to have it changed. In that case, it would be "den".
Someone correct me if I'm wrong, but I think it's because, in the absence of any context to inform its gender, a pronoun will default to neuter. Sometimes, even when there is context, it still defaults to neuter. "Hvad er det? Det er en ugle." Ugle is a common noun, yet the pronoun defining it in this case is still neuter.
Apparently what I have figured out my way is:
Kalder is specifically for 'when you call for someone', it could be help/support/or anything, like for example 'Drengen kalder på pigen' would be translated as 'The boy calls for the girl'.
'Drengen ringer til pigen' is more like 'The boy calls the girl'. This one is more used for phone context.
I hope it's understandable. :)