Employee charged with Breach of Contract

Good day! We have employees charged with Violation of Company Policy. IR was uploaded online and when NTE was served, employees refused to sign and submitted a resignation letter effective immediately. No disciplinary conference happened. These employees were charged with Breach of contract by their former Manager which is deductible from their final pay check. Former employees are now disputing the Breach charged to them. We've escalated this already to HR and they mentioned that BOC are usually charged to former employees whose resignation is voluntary and can no longer serve the notice period required by the company. The Manager is persistent that BOC should be charged. Would like to ask your expertise if our former employees dispute is valid? TIA

What are they disputing? That there was a breach of contract? If they had an existing contract with a fixed date and no "exit clause", then yes offhand i would say that they were in breach.