Json file update using PHP

Hello!
I'm trying to do this for several months without any luck. I have a Json file on my host server that I update from my website. I can delete and edit the array on the file but I cannot insert new data inside the array .
Example: I want to add a new player after "ID: 0" It does insert the new data but after after I put contents back and encoding the original file shows a duplicate. It creates another ID after the new data (a duplicate) and changes all other ids in the file automatically. Everybody says my code is correct but for some reason on my ends does not work properly>
Example: I want to add $list1 with id; "1" after id"0". It works but is adding another id; "2" after automatically.
Why is not working and adding a duplicate? Can someone find an fix my problem? Se codes attached