Whenever I conduct a live workshop or an online training, invariably someone asks the question "What should I say when my prospect says she's not interested?" My response is invariably "It's probably too late."
Certainly you can try to recover from the "I'm not interested" response. You can gently ask why (in a tone that says you're confused and really, really want to know the answer). If you ask why, prospects will explain what they mean, which can be very helpful for fine-tuning your pitch.
If someone says "I'm not interested," it can mean only one of two things:
You're not speaking with the right person, or
You're not saying anything interesting.
The time to address the "I'm not interested" challenge is before you hear it. From the moment your prospect says hello, your goal is to gain his attention so that he's hungry to hear more. If you can't get your prospect's attention, he will not want to speak with you. He will tell you he's not interested and may even hang up on you.
In order to get your prospect's attention, ask yourself these questions:
Who are you calling? Who has a need/challenge that your offering can solve? Prospects looking for solutions do not say "I'm not interested." Salespeople get into a lot of trouble by not thinking this through. (Hint: The answer is not "everyone.")