Refund from Employee Personal Expense Report

Hello,

We have employees that accidently entered personal expenses on their expense report, but didn't check the personal expense box. These employees (many whom departed the company) owe us this refunds back. They generally either send a check to one of our bank accounts or pay us via Paypal directly.

1. What is the best way to properly handle these from a process perspective?
2. Any report that shows the total personal amount owed and what payments have been submitted to offset the total amount owed?