I worked for a short time in a frum school that was under a chain of schools owned by the histadrut. The salary was paid by the chain. The last salary they gave me over 1000 shekel extra. I tried over the next month or two almost every day to get through to the secretary in charge – without success. I talked to a teacher there – he said they know about the mistake and I should talk to the secretary. I kept on trying – without success. At some point I tried less and less till I stopped. They have my number. I’m also in the phone-book. what should I do?
To ensure that you have told the right person, you should write a letter to the head office of the chain of schools, reporting that you have been overpaid, and stating that they should be in touch with you concerning how the money should be returned. Further to this, you have no obligations.
Sources: As with every case of hashavas aveidah, the finder is obligated to let the owner know of the find, and it is then up to the owner to collect it.