Yes, you can block unknown numbers from calling you. Most phone carriers offer this free service, usually included with your monthly plan. To block unknown numbers, add them to your list of blocked callers. This will ensure that they cannot call you again. If you receive unwanted calls from a particular number, you can also request that your phone carrier add that number to their do-not-call list. This will stop the caller from being able to reach you through your phone number. You can also file a complaint with the Federal Trade Commission if you believe phone calls are harassing you.