Não coloque nenhum dos parâmetros em seu texto de consulta com aspas!
->add('where', "c.owner = ?1 AND c.contact = u.id AND u.username LIKE '?2'")
deveria estar
->add('where', "c.owner = ?1 AND c.contact = u.id AND u.username LIKE ?2")
->add('where', "c.owner = ?1 AND c.contact = u.id AND u.username LIKE '?2'")
->add('where', "c.owner = ?1 AND c.contact = u.id AND u.username LIKE ?2")