SCAM - the IRS mails letters if there is a problem. They do not call!! www.irs.gov has an article on this scam. DO NOT give the caller any information!!
So who is "we"? This background info is not for regular forum users but for people who google this number after receiving a phone call looking for information about who is behind it. Hundreds of people are still losing money to these IRS scammers every week after it has been "known" to people like you for years. Do something about it.