BuddyPress.org

I want to remove member from a group when new user registered.
I have received group_id and user_id from database. then I want to remove all member from that group without group admin.
I used function ‘groups_remove_member’ in my own plugin .
I am new in wordpress and buddypress coding.
My code is
if (!function_exists(‘auto_join’)) {
function update_auto_join_status($user_id) {
global $wpdb, $bp;

// get list of groups to auto-join.
$group_list = $wpdb->get_results(“SELECT * FROM {$bp->groups->table_name} WHERE auto_join = 1”);

foreach ($group_list as $group_auto_join) {
$members_count = groups_get_groupmeta( $group_auto_join->id, ‘total_member_count’ );
if($members_count < 5)
{
groups_accept_invite( $user_id, $group_auto_join->id );
}
else
{
group_auto_join_hidden_group($user_id, $group_auto_join->id);
}
}
$wpdb->query(“UPDATE {$wpdb->users} SET auto_join_complete = 1 WHERE ID = {$user_id}”);
}

add_action( ‘user_register’, ‘auto_join’);
}

function group_auto_join_hidden_group($user_id, $group_id)
{

global $wpdb, $bp;
$utn = $wpdb->users; // Create a shortcut variable for wordpress users table.
$gmtn = $bp->groups->table_name . “_members”; // Create a shortcut variable for buddypress groups_members table.

$mysql = “SELECT user_id FROM $gmtn WHERE group_id=$group_id”;
$results = $wpdb->get_results( $mysql);
foreach ( $results as $user) {
groups_remove_member($user->user_id, $group_id);

}

}
my auto join working well but I am not able to remove member
Please help me what is wrong?