Unauthorised sim swap

Somebody made a simswap of my no then my fone was out of service.i went to MTN store in mall @newmarket where I was told that the swap was done on line and no verification was done.That completely surprise me I feel disrespected and I wasn’t given a case no instead I was just told to do a simswap.All of this resulted into my account cleaned out.pls help me get to the bottom of this.