Not sending Paid Up letter

My Gran Mother has been to Woolworths The Glen and paid my Late mothers Clothing account and has proof that there isn't anything owed and when she requested a letter from them stating that the has been paid in full and has been closed they tell her that they don't give letters and that the slip showing that the account is proof. That isn't proof because The Master Of The Court want settlement letters from all the creditors that my late mother had accounts with and owed money to. Woolworths is the only Creditor That say they don't give settlement letters. I can not accept that due to we need that letter to show The Master Of the Court.