Spam calls and robocalls have become such a problem that it's now expected that people will screen all their calls and not pick up unless they have identified the caller as someone they know. However, some may want to go further, blocking companies from calling in the first place. There are a number of ways to stop spam calls, and if none of them work, there is always the option of a lawsuit.
Go Through All the Basic Steps First
First, go through the basics: Sign up for the Do Not Call list, opt out of pre-approved credit card offers, and add spam-blocking apps to your phone. If you manage to speak with someone who is calling anyway, tell them clearly to take your name off of their phone list. All of these tools exist to reduce the number of companies calling you, and you will find a reduction in the number of calls. However, you may still get a lot of calls from companies that don't pay attention to the Do Not Call list or from companies that have simply decided to be aggressive.
Always Keep Records
Keep track of all the steps you've taken to get a company to stop calling you. You want this record partly to be able to tell who you've talked to before and partly as proof you did what you could to stop calls. If you have to file suit against a company for continuing to contact you, the notes will come in handy if they try to claim that you never told them to stop.
Allow for That Grace Period
When you sign up for the Do Not Call list or tell a company to remove your name from their call list, they do get some time to implement the change. This time allows them to ensure your name is removed from all of their lists and not just one list used by one call center.
Contact a Lawyer if Calls Truly Won't Stop
The Telephone Consumer Protection Act allows you to sue companies that continue to contact you via robocall or certain other methods when you've already asked them to stop calling you. You'll have to show you attempted to get them to stop and that you allowed for whatever grace period is required by law. But you're allowed to collect money for each time they contacted you after you notified them and after any grace period passed. Contact a lawyer if you think a situation with a specific company needs legal attention.