A taxpayer has reported a troubling incident where HM Revenue and Customs (HMRC) mistakenly refunded £2,500 to a fraudster impersonating them over the phone. Despite being in credit and having communicated with HMRC about the error, the taxpayer has received multiple letters claiming they owe the amount plus interest, leading to harassment from a debt collector. This situation highlights the vulnerabilities in tax systems and the challenges individuals face when dealing with bureaucratic errors.