Poor Workmanship and Service Advice

I recently serviced my BMW at Lyndhurst Auto in Johannesburg. The vehicle had a leak on the cooling system and as a result it was also booked in for repair/replacing of the cooling system. The service advisor called me and said that the expansion bottle cap was faulty and that is where the vehicle was losing coolant. The cap was then replaced. The next time I drove the vehicle the coolant light appeared. After investigating the problem myself I noticed that the expansion bottle was completely torn from top to bottom and all the coolant had leaked. I immediately phone the dealership and expressed my concern. The service department told me that they did not do pressure testing and just inspected the vehicle from the top after charging me for inspecting, finding leak and testing the cooling system. They would only see to the vehicle if I towed the car to them at my own cost and I would have to pay for further work. How can the service technician inspect the cooling system from the top only and charge a Client for doing a proper job? I have never received such bad service at a BMW dealership before. BMW head office I presume called to query the complaint but never got back to me.