Problem with javascript .change (it takes the previous data selected)

Question

I have a form:

Where I have a 'supplier' (proveedor) select that brings me the 'withholding' (retención) percentage that belongs to them when selecting it in the following way:

$(".js-proveedor-id").on('change', function() {

    var proveedor_id = $("#proveedor_id");

    $.ajax({
        url: "{{ route('get_proveedor_by_id') }}",
        method: 'GET',
        data: {
            proveedor_id: proveedor_id.val(),
        },
        success: function(data) {
            $("#retencion").val(data.retencion);
            retencion = data.retencion;
    }
    
});

    totales(retencion);
});

Now, my intention is that every time the select option is changed, it brings me the value of the withholding % and performs all the invoice calculations again; but for some reason it is not taking me the change of the retention value until I change the select again.

For example: I select a provider with 100% retention and add the items I want and everything works, but if I want to change the provider and select one with 0%, no change is made until I select another one again and it reflects the calculation with 0% retention; it's as if it's keeping the previously selected value.

If I add another item after selecting another provider, the withholding % is updated; but when changing it or deleting an item, no.

My totales() function:

function totales() {

    retencion = $("#retencion").val();

    $("#subtotal").html("$ " + subtotalapagar.toFixed(2));
    subtotal_pagar = subtotalapagar;
    $("#subtotal_pagar_html").html("$ " + subtotal_pagar.toFixed(2));
    $("#subtotal_pagar").val(subtotal_pagar.toFixed(2));

    impuesto = subtotalapagar * 0.16;
    $("#impuesto").html("$ " + impuesto.toFixed(2));
    impuesto_pagar = impuesto;
    $("#impuesto_pagar_html").html("$ " + impuesto_pagar.toFixed(2));
    $("#impuesto_pagar").val(impuesto_pagar.toFixed(2));


    retencionapagar = impuesto_pagar * (retencion / 100);
    $("#retencion").html("$ " + retencionapagar.toFixed(2));
    $("#retencion_pagar_html").html("$ " + retencionapagar.toFixed(2));
    $("#retencion_pagar").val(retencionapagar.toFixed(2));

    total_pagar = subtotalapagar + impuesto_pagar - retencionapagar;

    $("#total").html("$ " + total_pagar.toFixed(2));

    $("#total_pagar_html").html("$ " + total_pagar.toFixed(2));
    $("#total_pagar").val(total_pagar.toFixed(2));

    tasa = $("#tasabs").val();

    total_pagarbs = tasa * total_pagar;

    $("#totalbs").html("Bs. " + total_pagarbs.toFixed(2));
    $("#total_pagar_htmlbs").html("Bs. " + total_pagarbs.toFixed(2));
    $("#total_pagarbs").val(total_pagarbs.toFixed(2));
}

and eliminar():

function eliminar(index) {
    retencion = $("#retencion").val();

    subtotalapagar = subtotalapagar - subtotal[index];
    impuesto = subtotalapagar * 0.16;

    retencionapagar = impuesto * (retencion / 100);

    total = subtotalapagar + impuesto - retencionapagar;
    total_pagar_html = total;

    $("#impuesto").html("$ " + impuesto.toFixed(2));
    impuesto_pagar = impuesto;
    $("#impuesto_pagar_html").html("$ " + impuesto_pagar.toFixed(2));
    $("#impuesto_pagar").val(impuesto_pagar.toFixed(2));

    
    $("#retencion").html("$ " + retencionapagar.toFixed(2));
    $("#retencion_pagar_html").html("$ " + retencionapagar.toFixed(2));
    $("#retencion_pagar").val(retencionapagar.toFixed(2));

    subtotal_pagar = subtotalapagar;
    $("#subtotal").html("$ " + subtotalapagar.toFixed(2));
    $("#subtotal_pagar_html").html("$ " + subtotal_pagar.toFixed(2));
    $("#subtotal_pagar").val(subtotal_pagar.toFixed(2));

    $("#total").html("$ " + total);
    $("#total_pagar_html").html("$ " + total_pagar_html.toFixed(2));
    $("#total_pagar").val(total_pagar_html.toFixed(2));

    total_pagarbs = tasa * total;
    $("#totalbs").html("Bs. " + total_pagarbs.toFixed(2));
    $("#total_pagar_htmlbs").html("Bs. " + total_pagarbs.toFixed(2));
    $("#total_pagarbs").val(total_pagarbs.toFixed(2));

    $("#fila" + index).remove();
    evaluar();
}

What I don't understand is why if it changes the value of the input inside the form (where it says % de retención it writes the number taken from the database) but it doesn't take that same value inside the totales() function