Lists the last name of all clients who made a PS-type complaint and were served by TOVA.
PS-type complaint refers to type = 'PS'; served by refers to server;


SELECT t1.last FROM client AS T1 INNER JOIN callcenterlogs AS T2 ON T1.client_id = T2.`rand client` WHERE T2.type = 'PS' AND T2.server = 'TOVA'