Don't answer! Let me give everyone a helpful tip here: never answer a phone call unless you know who's calling, or until you've looked up the number first to be sure it's not a telemarketer.
The minute you answer a telemarketing call, that tells them you have an active phone number. (Ever gotten calls with no response and nobody speaking on the other end? This is a tester call to see if you pick up. They save the phone numbers of people who answer tester calls.) They will call your phone several times to try to get you to answer. An active phone number means a potential customer.
If you NEVER answer, what can they sell to you? Nothing. They take that hint and move on.
Don't call back, either. No telemarketer will honor your request for them to stop calling. They don't care if you get angry.
I added my name to the do-not-call list a few years ago but it does nothing. The only thing that works is never answering their calls. Eventually, they WILL stop bothering you. If you never answer, their efforts trying to call you are a waste of time and potential money they could get from calling someone else.
Trust me on this. I used to get telemarketing calls like crazy, but now I hardly get calls from ANY of them. It's annoying that they call, but calling them back to yell at them is going to do absolutely nothing to help your cause. Just don't answer and move on with your day. Don't let it bother you. Over time you will notice a sharp decrease in the amount of telemarketing calls.