My mother got a call from this number and since she does not speak English she gave a caller my phone number (she knows the numbers in English). He called me and said my mother committed a fraud and she owes money to IRS. I asked why didn't they send a letter explaining what the matter of fraud was. They answered that they sent papers by FedEx 3 times but nobody was home to get them, which is not true - my other is 86 y. o. and she does not leave home. They said my mother owes $2,500; however, upon payment she would receive a tax return in the amount of $5,800. I requested  a letter again and the caller said they would send 2 lawyers to my mother's apartment to resolve the matter.
The whole conversation sounded very suspicious to me. I said I did not believe he was calling from the government and just hung up. Then I started my own investigation and found out the caller called from a mobile phone. Then I found this page..