If you did not spend any of the "overage" paid your grandmother after her passing but rather your aunt did, then you should not be responsible for the reimbursement of these payments to the retirement plan, your aunt should be.I would write the retirement plan as to what transpired as to the spending of the money after your grandmother's death and request a written response in return. You need to keep a copy of the letter for future reference. I would also speak with your aunt about the need for her to repay the retirement account for payments made after your grandmother's passing that she used.