Bad service

In 2014 I purchased a brand new Datsun Go from Northwest Nissan in Princess Crossing. I have been driving my car for three years taking it for service on the required kilometers. I had slight difficulties with the key but it was functioning until recently when the key would not unlock the car when I compared the spare key with the key I have been using I saw that there was a slight difference they did not look the same. I went back there to find that the staff was new and they told me that the key was worn out and they said that I must buy another key. The warranty pages on the service book had not been filled in until today 23/08/2017. I cannot buy a key that I did not damage the key clearly shows that it has a manufacturing default. It cannot be worn out in three years where as the key of a 14 Year old car still works and has not been worn out. I will not buy a key Nissan needs to replace this key before I take further steps because even the manager could not be of any assistance to me.