How do I block a number from calling or texting my cell phone?

I don't want to have to get my number changed. My phone is with AT%26amp;T...can I just walk in the store and give them the number and pay a fee and make it where they can't call or text me anymore?How do I block a number from calling or texting my cell phone?
Just call customer care--611 from your phone. They can do it over the phone.How do I block a number from calling or texting my cell phone?
call your service provider- they can block certain numbers from calling/texting you.