NON PAYMENT yet services provided in full

I supp**** a driver to Speck Pumps in Cape Town. They used him for quite a long period of time. I sent them invoices weekly but they failed to pay them according to their terms and conditions with us. They then stopped using the driver as they sourced one of their own.They paid their account but failed to pay a substantial amount. When I inquired as to why, they came with some long story about our driver *****ing a \piece of a pool pump"and this is why they have not paid this amount. As they were fully aware that should an incident occur with any of my staff at their premises we need to be informed within 48 hours of the incident occurring"