Netstar lack of consistency and transparency

I traded in my car and alerted netstar so that they can arrange to have the new car installed with a netstar since my contract it's still active. They are charging me just over R600 for the process, mind you I have a friend who did the same on the same day as me and was not charged a cent for the process. When I called netstar to enquiry about their inconsistency the lady told me that I should not compare myself to my friend, we may have the same netstar plus tracker but I am not my friend so i should pay the said R655 service fee. So, does the service fee apply to certain people and not all clients? What is the criteria used? I'm disappointed with Netstar, I wish I had not upgraded my tracker with them last to a new device and continued with a month on month payment terms.