Standard bank gives my personal information to another client without my consent

A person mistakenly deposited money 600 into my Standard Bank account, after a day or two of trying to figure out who the money was from and no avail I decided to use the money. Now two weeks later the person goes to the bank and Standard bank decides it makes logical sense to give this person my private cell phone number where now I'm getting odd calls. My biggest problem here is how does such a large institution like that give out our personal information to strangers without having consulted us. This is pure nonsense. The bank always send out messages to say we must not give out our details to strangers and they go and do the exact same thing. Is this how banks operate now.