How do you block someone from calling you on a Palm Centro 385?

I singed up for a home makeover sweepstakes, and this girl keeps calling me about it. I got the chance to actually answer, and she was asking if I had a credit card. I kept saying no to her questions, and she said are you under 18, and I hung up. I'm under 18, but my mom told me I could, so it didn't matter. I still don't want her to call me, its been getting very annoying.