I've received a overpayment letter from tax credits because of my ex husbands income. He left in November and I declared this and gave all info requested. My tax credits as a lone parent were reduced and life went on. I completed my renewal in June and received a letter saying nothing was owed either way but then 2 weeks later received an overpayment letter for £1850 because my ex husband declared his commission only based income for the last tax year. I can't afford to pay it! Or half as they've told me. I get no maintenance payments from him (because he's a waste of space) and i work part time because of illness. Any ideas how I can fight this successfully?