Hi,
We are unable to investigate your request fully without a NINO of your mother or father. I’d recommend contacting the Tax Credits helpline with your mother available to answer security questions. The advisor should be able to assist with what was claimed for, how long, when the claim ended, if it ended correctly, and give details about the debt.
Where details of the Tax Credits claim appear incorrect, you can dispute the overpayment on gov.uk. More information on how to do this can be found here:
Tax credits: appeals and complaints
As the debt has transferred to DWP, the recovery should be discussed with them. More information on how to contact them is available on gov.uk. This link may be useful:
Repay and manage benefit money you owe
Thank you.