Unsolicited calls

The calls started 2 weeks , the calls come from various area codes. They insist on speaking with me, when I ask the nature of their business, they get nasty and insist that I tell the, who I am. I do not tell them and advised that as they are calling my phone, it is they. Who must identify themselves.
I called them and a recorded message said that I was eligible for a $100 gift, they also provided the opportunity to unsubscribe, which I did by entering my phone number.