I got a letter not long after my renewal letter saying I owed £300 from tax year 2011/12 . I thought I'd just wait until after the 31st July to Phone them because of how busy the lines are . But I've just got a letter from a company called Sigma saying they debt has been passed on to them . Can I still phone tax credits to pay the debt ? Is it even legit ? Also will it affect my credit rating that's already in the shit anyway 