You need to get help from an expert in the filed in your area to determine if in fact an overpayment was made and then what the law states as to the outcome.  Certain types of over payments must be repaid (unemployment is definitelyone) and your rights and liabilities have to be made known to you.  There may not have been an overpayment as you say so I would not panic as of yet.  As for you right to you vacation pay, the company is waiting to see the determination before using it to off-set their liability.  These types of pays, however, may or may not be intertwined but I would go for requesting it now.  Just hold on to it should you be found to have to repay.  And given your limited income you may have a right to reduction if the error was theirs.  Also, speak with the attorney about the "terminated due to disability" statement. Just to be sure it was legal.  Good luck.