As the tax filing deadline approaches, the Rhode Island attorney general's office is warning about an increase in the frequency and aggressiveness of IRS scam phone calls.  People have reported receiving frequent calls threatening immediate arrest for failure to make a payment for supposed owed taxes.   Since the scam first surfaced several years ago, authorities say the technology scammers use to appear they are calling from the IRS has become sophisticated.  Anyone receiving such calls is advised to hang up and contact the the attorney general's consumer protection unit.