Avoid double registrations in Javascript

The cause of the problem is quite similar to this other question . I'm going to put a reduced version of the code you have in JSFiddle here:

$('#upload').on('click', function(){

  // código y operaciones
  // abrir modal
  // más código y operaciones

  confirm.on('click', function(){
    // pedir confirmación
    // serializar la tabla
    // petición AJAX y cerrar modal
  });

});

The button with ID "upload" is responsible for opening the modal, and the button with ID "confirm" is that it performs the AJAX request and closes the modal.

As the association of the event handler click of the "Confirm" button is done within the click event of the "upload" button, this means that a controller will be associated with the "confirm" button every time click on the "upload" button.

Let's see it step by step:

Do you see what is happening? Each time you click on "upload" the same controller that makes the AJAX call is associated again and that is why you end up saving the data multiple times (as many times as you have clicked on "upload").

The solution: as the modal already exists on the page and what is done is to show / hide it, you do not need to associate the controller of the click to "confirm" each time the modal is opened, it is enough that you do it once at the top of the page:

$('#upload').on('click', function(){

  // código y operaciones
  // abrir modal
  // más código y operaciones

});

confirm.on('click', function(){
  // pedir confirmación
  // serializar la tabla
  // petición AJAX y cerrar modal
});

Try this and tell me how you are doing.