True, you can block certain numbers. However, the hounders have several tricks to get around that. The most common is to call from someone else's house. This means they don't have to call from the blocked number, and they get through. They can also use their cell phone, change their number, or mark a call as particularly urgent. These are effective in getting around the block.
If you have Caller ID, preferably with the feature that allows the name to come up, you have a better chance. That way, even if they change the number, the name is still the same and you will be able to screen it. If they call from another person's home, chances are you will recognize that person and be able to block that one, too. If they use a cell phone, they will also have the name. And private name/private number calls are always suspicious, since they often mean telemarketers anyway. This is not perfect, but it will stop them from being able to change numbers or call from another "friend's" home.
Of course, if you don't mind being rude, you can always hang up on them. If you answer the phone and it is the hounders, there is the hang-up button. They will probably call back, and they will either not get an answer or they will get hung up on again. Unplugging the phone from the wall jack works just as well--when they try to call back, they will just keep getting a busy signal. Using dial-up Internet or taking the phone off the hook when you are expecting them to call back works as well.
None of this matters if you get paper letters. The regular ones are easy to discard as junk mail. If you get one certified mail return receipt requested and see the address, then you will need to refuse it. They will soon get the message after getting a few of those back, since it will waste their postage. It will not stop them from sending you spam--putting them on your spam blocker will only work until they change the address. Either way, you have to report it as spam--hopefully, if they send enough spam, they will lose their Internet service for spam.
