Forklift Spares Specialists not so Specialized

An employee tried to fix our forklift with a disastrous modification. He used an old inverter and battery used for a TV and also cut wires and replaced it with unspecified products. Forklift Spares Specialists Silverton was appointed to repair. They put a battery which is about 30% of the specification size into the machine and connected this to the modified items. This obviously didn't last a single loading session. For the exchange of this battery which costs R2300-00 on the shelve, they were paid R7500-00 as per invoice. At the time of invoicing the machine was closed up again and we didn't see the mess inside. The battery was returned to them. The owner doesn't want to take any responsibility and refuse to refund us. They have no technical skills, and their business ethics is one of the worst I have encountered.