I had a car dealer salesperson who followed up a couple of times. I just told her I decided not to buy a car.
For the future, you can get a Google Voice number for free, and don't set it up to ring to any phone. That's how I have mine, so when they call and leave voicemails, I get an email and just go to the Google Voice page and listen to them, or see a transcription of them. Then if you see the same person contacting you over and over, and you don't need to call them back, it's as easy as deleting an email or an IM. I have also saved the ones where I was required to report back to the MSC whether the person contacted me back or not, in case the MSC follows up later to ask about it.