If your service is through cable, you can use
NOMOROBO filtering service.
If not, it's good to have a caller ID service that allows you to see who's calling. If you have an answering machine or voice mailbox and don't recognize the number, let it go to the voicemail or answering machine.
When you answer a scam call, you are verifying that it's a valid number and setting yourself up for further calls. Additionally, some calls will leverage your phone line so it's best never to wait on hold, be transferred or even talk to someone. I know it's tempting, but if it really is a service you have, you should be getting emails or mail correspondence. Very few legit companies will call you to verify your information or inform you of an offer. In most cases those are Phishing calls, trying to get your info for identity theft scams.
TM