My antenna motor is working but the antenna has.

Do you mean the antenna motor runs constantly? If it is, it will overheat eventually and the entire assembly will have to be replaced. On most antennas, you can unscrew the nut on top with a special socket, then turn on the radio and ignition switch, then pull up on the antenna while the motor is running. When you pull it far enough, the plastic notched cable will pull out too. For Chrysler products you can buy just the mast with the cable. I suspect your Nissan dealer can order the same part. Feed the cable into the tube as far as it will go, then have a helper turn the radio off. As soon as the motor runs the cable down push and guide it in. Once the base of the mast is in the tube, you can reinstall the nut. Don't worry if the mast didn't go all the way in. It will self-adjust after you run it up and down once more.

Just to add this one they sell the repair kits mast with the tape with instructions there pretty cheap I got one for a pathfinder for 14. Pretty simple install unless the new mast doesnt go all the way down if that happens you will have to pop the cover off the assembly and remove the old broken piece of the plastic tape that runs the mast.

Most likely the cable is stripped. Visit the dealer to see if they can still order the replacement mast.

Ebay has them iam sure there cheaper than the dealerand good quality but its up to you how you spend your money.