I change my Xbox gamer tag but on fortnite my old one is still showing

Again, contacting support won't change anything. The IA is giving you incorrect information. Since you have a special character in your new tag, you'll have a "classic" gamertag tied to your account as well which is your old tag. Your old tag will show in any place that has not been updated to work with the new gamertag system. That's why you see it in the game.

No I changed like a month ago

Do you I should call Xbox support?

This is my fortnite user ᴸᴹᴷ Paly ネ

That's odd, could you try double check your fortnite username to see if maybe you need to change it instead?

Log into Epic Games, go to Account, and click the blue pencil icon to edit your Display Name > Save Changes.

In case you need more detailed info or steps you can check this article:
https://www.lifewire.com/change-your-name-in-fo....

** This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.