Tell HM Revenue and Customs (HMRC) if you’ve received too much tax credits and don’t think you should have to pay it back because you met your responsibilities and they didn’t meet theirs. You can either:
use the online form service (sign in to, or set up a Government Gateway account)
fill in form on-screen, print it off and post it to HMRC
If you use the online form, you’ll get a reference number that you can use to track the progress of your form.
You must be able to show that the Tax Credit Office made a mistake, or gave you incorrect advice, and it was reasonable for you to think your payments were right.