Won esa appeal query on backdated money

Hi I won my esa appeal back in Nov and received letter today from dwp stating there are due my over £800 dating back to my failed assessment in may this was what I was expecting however the letter states that as I owe them over £5000 due to a previous overpayment which I had already agreed a deduction amount each week they say that they are taking the £800 and using this towards overpayment I cannot believe this I borrowed money from family over Xmas as I knew I was due backdated money is there anything I can do ??
Many thanks

The following explains what the DWP can do

www.turn2us.org.uk/information__resource...ns/overpayments.aspx

If you have back payments outstanding then the DWP can use this in addition to your weekly payments, so if your debt is more than the £360 you say they owe then they can offset this against it.