Block the texts and calls. Check the emails, some of them have an unsubscribe on the bottom. If not, respond to the email and say that you bought a car somewhere else and to remove you from the contact list.

I clicked interested on a car on autotrader and the dealer is contacting me every hour from 9-5 for the last week. text email and voicemails.

I honestly am not interested at all it had the opposite effect and I want to go to carmax and not deal w/ them even though I could haggle it down a few thousand