Telemarketing calls

We own a small business and we have an account with an "other" phone company, not AT&T. We receive calls on a daily basis from AT&T, we have asked them NOT to call us anymore, yet they still do. When they call and ask for the person in charge on the phone account, and we state that they are not available can we take a message they become rude and say no message we will call back and hang up before we can say anything. At one time, when they were told that we were not interested, they man asked if he could ask who we were using as our phone company, the other secretary told him and he laughed and hung up! The other day 2 gentlemen showed up at the door and introduced themselves as being with AT&T and that they were here to talk to the owner about the phone account. When I told them that he was not here, they immediately acted appalled and said that they 'were suppose to be here today and this time to meet with someone'. I said, funny since I am the only one who makes appointments here and I knew nothing about it, I told them we have a 5 year contract with another company and that we are not interested. They continued to tell me that they reduced rates and when could they come back to speak with the "person who handles the account". I told them not to. These people are relentless and rude.