Delta-Sigma Inc

I keep receiving phone calls ( I might say aggressive calls) by a man at this number looking for the President of the company. I have asked him the nature of the call and he either hangs up or states that he will call back at a later time. I have asked him numerous of times to please remove us from his calling list and he has yet to do so. I am extremely frustrated to have someone call and harass me and give me a hard time for doing my job. Needless to say - very bad business manners !!!!!!!