manager harrased me and comes to my company

I came to hifi corp to swop a phone, so the staff members swopped the phone for a gift card because according to the hifi policy we stock it we swop it . three days later I get a rude call from the branch manger MR (VERDIE ANDREW) saying I must return this card immediately I tell him im off and why are you being rude he tells me that's my business and tells me he knows me and where I work and his coming to my company,so I told him that im not at work he tells me im going there any way, 1stly what gives him the right to to come to my work place. I have spent thousands in your store as a customer , who gives him the right to feel that my personal life is any of his business . who gives him the right to tell my colleagues this is not healthy for business for do I come across you as a child or an uneducated person that stole or tried to run away.now I have to deal with people asking me why where they looking for you. unfortunately I don't know all the procedures the company as I am a customer not a staff member then he threatens me that people will loose their jobs as if I have friends working there or I *******ly did some thing . I sincerely hope this will be dealt with.