No, dearest, you don't need to be alarmed. The IRS never calls, they use the mail. They probably don't even have your address or real name. Rather than block this spoofed number, just don't answer it. If you block it, they will just get under your radar again with new phone numbers... Better the devil you know than the devil you don't. When you see this number again, just recognize it and ignore the call.
... And why are you telling them here to stop calling you? Do you really think they know who you are? Do you think they come to 800notes to see and heed your request, when all you reveal here is a screen name? When you go to the movies and the "coming attractions" says "coming soon to a theater near you," do you also think they know what town you are in and your individual identity? Don't answer the call: memorize the area code or prefix and don't answer the call when you check your caller ID.
Answered this call. Told them I'd pay them all of my unpaid back taxes via bank draft, if they promised to never spam all these fine people ever again with incessant phone calls. They agreed. You're welcome gang!