DB Queries not working

I’m building a plugin that adds and removes data from a very simple table. I built the queries, called the methods on $wpdb, but the database does not change.
When I output the last query after I run the queries and copy-paste it into phpMyAdmin, they work fine.

Here are the key functions:

private function remove_from_db( $s_table, $i_item_id )
{
	global $wpdb;
	// get table name
	$s_table_name = ($s_table == 'cart')
		? $this->s_cart_table_name
		: $this->s_wishlist_table_name;
	// get user id
	$i_uid = get_current_user_id();

	$s_query = "DELETE FROM {$s_table_name} WHERE uID={$i_uid} AND wID={$i_item_id};";
	$wpdb->query( $wpdb->prepare( $s_query ) );
	//echo $wpdb->last_query;
}

private function add_to_db( $s_table, $i_item_id )
{
	global $wpdb;
	// get table name to insert into
	$s_table_name = ($s_table == 'cart')
		? $this->s_cart_table_name
		: $this->s_wishlist_table_name;
	// create an array of values to be inserted
	$a_values = array(
		'wID' => $i_item_id,
		'uID' => get_current_user_id(),
	);
	// insert values
	$wpdb->insert( $s_table_name, $a_values );
	//echo $wpdb->last_query; //echo 'dadada';
}