NTT Nissan Newcastle, Kzn, Refusing to Service a Vehicle Under Warranty

A booking for our NP300 for it's 1st service was made with NTT Nissan Newcastle on the 4th March 2021, This vehicle is still with the dealer as of 30th March 2021 and not serviced without a reason. I called with other Nissan vehicles to make bookings with the same dealership and the appointments were made. I cannot understand why a vehicle which is still under warranty cannot be service at this dealership. We are fleet owners. Spoken to Nissan customer complaint and DP himself with no success. Not sure if my color must be changed to have them to assist me.