Solved it by replacing the currency symbol all together with a custom option inside an ACF radio button:

function cambiar_currency_symbol( $currency_symbol, $currency ) {
    $currencyacffield = get_field('moneda');
    switch ( $currency ) {
        case 'USD': $currency_symbol = $currencyacffield; break;
    }
    return $currency_symbol;
}
add_filter( 'woocommerce_currency_symbol', 'cambiar_currency_symbol', 10, 2 );

Tested and working.