A robocaller’s phone number rotates because they use a Voice-Over Internet Protocol service overseas. Blocking the phone number does very little to prevent robocalls.
Depending on your carrier, you may have to pay for call blocking. You may also have to pay to get more premium features (such as revealing phone numbers of unknown callers).
Ask for the caller’s name and company (including phone number and contact address) and reason for calling you. If this is not provided to you within 10 seconds, hang up. Chances are, it’s a scam. Type the address or phone number into Google. The first result had better be them. If it’s a real company, then they will happily give you their contact information. If you can’t search while talking at the same time, ask the caller to hold on for a minute for a personal matter, but use the time to check out the company on the internet. If it doesn’t exist, immediately be suspicious. You could also look for feedback about the company or type of call. Government sites aimed at revealing scams may be helpful here too. You can even be polite. For example, ask them for their phone number, extension, and what this is regarding. Then let them know that you will call them back. If they do give you a phone number never call them back at that number. Use that number to look up the company and use the company’s contact number to call them back. The number they give is likely phony. Real companies want you to call them back. Sales calls are more likely to make a sale if you call them. And banks get a thrill when customers practice real security by calling back on the bank’s official support number. If the caller pressures you to stay on the line, then it is a scam. If you get a “political survey” from a “non-profit”, then confirm by using the IRS’s website. Select the type of form (8871, 8872, or 990. If you don’t know, just select all three) and enter the organization’s name. If the search does not identify the organization, then they are not exempt. Also compare phone numbers. If none of the details match, then it is likely a scam.
If you have identified yourself and greeted the caller but the caller fails to acknowledge this and speak instantly in a conversation, but asks to speak with you, suspect that they are transferring you between sales teams or the like and are not someone who knows you.
A real company won’t hang up on a prospective or existing customer. Remember that.
They do not know anything unless if you were tapped or if they installed rootkits on your computer.