How to Handle a Former Employer's Unexpected Payment Demands After Termination?

Background of the Situation

My brother was employed in the India sales team for a Europe-based B2B travel company. He was recently asked to leave the organization with immediate effect due to some allegations made against him. His side of the story was not heard by the directors, and because he was not paid much due to the COVID-19 situation, he agreed to resign by settling the necessary dues to the company and returning the company assets. However, when he requested an experience letter, the company directors delayed it and later accused him of fraud in some files where his friends or family had traveled. They claimed that adjustments were made in those files from some other files, which were based on conversations with some of the directors but were not recorded. Now, the directors are writing emails to claim amounts from my brother for those files.

Access Denied to Files

When he asked to regain access to his machine/laptop to check the stated and related files, they denied the request but mentioned they would share all necessary information over email, some of which dated back 3 years. Accessing files over a 3-year period and providing justification without any payment did not make sense, so my brother denied the request.

Company's Pursuit of Payment

The directors are now sending emails stating, "Rest assured that we will pursue this matter until every cent and centime has been repaid." The original agreement my brother signed with the company does not include any clause about payment to the company or the employee being answerable to the employer for any inquiries post-termination.

Seeking Advice

What should we do?

Directors' Actions and Allegations

Further to this, the directors of the employer are now reaching out directly to the friends and family members who traveled, claiming that it was identified in an audit that the payment is due from their end and they should settle it immediately.

It seems that the intention is either (1) to extract the money from the travelers (which is unlikely as they have already paid their part and the company would not have allowed them to travel or given travel vouchers if that was not the case) or (2) the directors want the travelers to explicitly state that the money was handed over in cash to my brother and use that as proof against him that he never submitted that money to accounts. Without access to his mailbox, my brother has no proof against them to prove otherwise.

Cash Handling and Reporting Issues

Now the catch here is that cash was not supposed to be accounted for in India; it was supposed to be transferred/handed over to the Europe branch and reported there by the Accounts based on confirmation from directors. However, several times directors had not reported cash immediately to adjust in other transactions.

Looking forward to some guidance, please. Thanks in anticipation.