collection process for an amount in dispute?

To make a long story short, I was in a social organization that charged membership dues. It was an undergraduate organization for the college I attend. Once I recieved my acceptance into the graduate program and that semester ended I ended my paying of dues to that organization. I was to be considered an alumni and was still able to participate in certain activities, which is not uncommon. I was however unable to vote, because I was not paying dues. The following semester I and this organization had a falling out and I am no longer active in the organization. However, now the organization is threatening to send me to collections for un paid dues, only come to find out they have been charging me dues for 3 months after I was a graduate student. I feel like nothing is going to come of it, but if they do send my alleged outstanding balnace to a collection agency does it automatically go on my credit history even if I dispute the amount in full? I have great credit (over 720) and do not want to lose it because some people are trying to "get even". What is the process for collections and how do I dispute the collection.

If I have all of the appropiate documentation regarding when I was accepted into graduate school and provide the collection agency with a copy of the organizations constitution which clearly states "undergraduate" organization, will that be sufficient proof I should not have been charged for any dues after the semester I was accepted into grad school ended? I guess it should be said I started grad school the following semester.