What is the ruling regarding someone who used to pay a portion of the money for phone calls at a university switchboard affiliated with the government, but did not return the remaining portion, and the official in charge does not remember to claim it, and how can she return this money?

The questioner must strive to estimate the wealth until she is reasonably certain that she has encompassed it. Then, she should pay the amount to the usual authority if she knows it will reach its rightful recipient. However, if she knows it will not reach them, she must give it as charity to the poor or spend it on good causes and the general welfare of Muslims.