/**
 * AUTO COMPLETE PAID ORDERS IN WOOCOMMERCE
 */
add_action( 'woocommerce_thankyou', 'custom_woocommerce_auto_complete_paid_order', 10, 1 );
function custom_woocommerce_auto_complete_paid_order( $order_id ) {
    if ( ! $order_id )
    return;

    $order = wc_get_order( $order_id );

    // No updated status for orders delivered with Bank wire, Cash on delivery and Cheque payment methods.
    if ( ( 'bacs' == get_post_meta($order_id, '_payment_method', true) ) || ( 'cod' == get_post_meta($order_id, '_payment_method', true) ) || ( 'cheque' == get_post_meta($order_id, '_payment_method', true) ) ) {
        return;
    } 
    // For paid Orders with all others payment methods (with paid status "processing")
    elseif( $order->get_status()  === 'processing' ) {
        $order->update_status( 'completed' );
    }
}