SELECT u.id,eb.caption AS "brands_name",t.start_at,t.end_at #отказники
 FROM users u
LEFT JOIN transactions t
 ON u.id=t.user_id
WHERE t.content_type_id IN(1)
AND t.end_at>'2018-01-01' AND t.end_at<='2019-01-01'
    AND NOT EXISTS (SELECT u1.id FROM users u1,transactions t1 WHERE t1.user_id = u1.id AND t1.status_id = 2 AND t1.start_at >= '2019-01-01' AND t1.end_at>'2019-01-01' AND t1.content_type_id IN (1))

NOT EXISTS (SELECT u.id FROM users u,transactions t WHERE t.user_id = u.id AND t.status_id = 2 AND t.start_at >= '2019-01-01' AND t.end_at>'2019-01-01' AND t.content_type_id IN (1))