Urgent matter

I am very upset with Fnb, someone that I don't know, deposited an amount of R7000 into my account on Saturday 01/03/19, I don't even know that person, now my account has been freezed without even consulting me, this person that deposited money Into my account, then called Fnb and instructed them to freeze my account, how does a person that I don't even know call Fnb and instruct them to freeze my account..... Now the question is: how safe am I as an Fnb client? If fnb ***** department can freeze the account without even calling the right full account holder? Now I have been advised that my account is being investigated as I went to the branch In South Gate today.... ********** 548