If you are getting the username with bp_get_displayed_user_fullname()
function, that returns you as a string value.
$wpdb->get_results(
"SELECT * FROM `wp_shipping_numbers` WHERE `username` = $ttm_username "
);
Use
$wpdb->get_results(
"SELECT * FROM `wp_shipping_numbers` WHERE `username` = '".$ttm_username."' "
);