Reserved funds

May someone please help me.FNB decided to reserve R5000 from my account without even notifying me.Days letter I recieved an email from someone saying they have reserved R5000 because I recieved money from someone which had traces of *****.How am I at fault because I just recieved money and nowi am being held at random because of something that I dont know.Please FNB resolve my issue I need to recieve my salary from that account in a few days time.