Wrong number calls several times per day...how can I block them?

I have a motorola Razor and receive calls on and off from people who yell at me in Spanish. I tried to tell thim that it is the wrong number and even used my limited Spanish comprehension to tell them so, but they continue to call and leave messages when I don't pick up. Is there any way to block them? I have gone on translation sites to learn how to say this is the wrong number, stop calling, but am sick of wasting my time.