Override custom prices in cart/checkout

Hi, I wrote a function to customize product prices, but I need to edit them inside cart and checkout page. The problem is that nay function that tries to edit the prices inside the cart, don’t work, I think because there is the other filter that already changes the prices: there is probabily a conflict I don’t know how to solve.

FUNCTION THAT CHANGE PRICES GLOBALLY

function product_custom_price($price, $product) {
if ( ! is_page( 'cart' ) || ! is_cart() || ! is_checkout() || ! is_page( 'checkout' ) ) {

		$custom_price = $product->get_regular_price();
		$my_current_lang = apply_filters( 'wpml_current_language', NULL );
		//ITALIA 
		$ssivata = 7.93;
		$ivaitaperprezzofabbrica = 122/100;
		$arrotondamento = 4/10;
		if( $my_current_lang =='it' ) {
		$tax = 122/100;
		$shipping = 6.5;
		}
		if( $my_current_lang =='at' ) {
			$tax = 120/100;
			$shipping = 24;
		}
		//calcola prezzo di fabbrica
		$custom_price1 = $custom_price - $ssivata;
		$custom_price2 = $custom_price1 / $ivaitaperprezzofabbrica;
		//calcolo del prezzo
		$custom_price3 = $custom_price2 + $shipping;
		$custom_price4 = $custom_price3 * $tax;
		$custom_price5 = $custom_price4 + $arrotondamento;
		return round($custom_price5,0,PHP_ROUND_HALF_UP);
	}
}
add_filter('woocommerce_product_get_price', 'product_custom_price', 10, 2);
add_filter( 'woocommerce_product_variation_get_price', 'product_custom_price', 10, 2 );
add_filter( 'woocommerce_product_get_sale_price', 'product_custom_price', 10, 2 );

FUNCTION THAT should CHANGE PRICES IN CART (the value of the price is just for test)

if ( is_page( 'cart' ) || is_cart() || is_checkout() || is_page( 'checkout' ) ) {

add_action( 'woocommerce_before_calculate_totals', 'add_custom_price', 20, 1);

	function add_custom_price( $cart_obj ) {

		// This is necessary for WC 3.0+
		if ( is_admin() && ! defined( 'DOING_AJAX' ) )
			return;

		// Avoiding hook repetition (when using price calculations for example)
		if ( did_action( 'woocommerce_before_calculate_totals' ) >= 2 )
			return;

		// Loop through cart items
		foreach ( $cart_obj->get_cart() as $cart_item ) {
			$cart_item['data']->set_price( 40 );
		}
	}
}