Plumber overcharging client with no feedback.

Good day. Fogi is a third party company that do emergency work for client's insured with Virseker. They came to my property to fix a small water pipe leak on an outside water pipe. It only took 20 min to complete. I was then issued with a invoice of R700.00. When I asked what this is for I was informed that is for the material used. I was supervising the plumber and knew that only two 15mm flanches were used they cost R7.00 each. I confronted the plumber, he then phoned Fogi and the invoice was reduced to R285.00. I then phoned Fogi myself. I asked them for a detailed invoice stipulating the material used, I also told them that the material could not have been more than R15.00. They never returned my call or send me a proper invoice as was requested. I refused to pay the invoice. I followed this up with Virseker, they told me that the amount also included the labour?? This was an emergency service covered by by comprehensive insurance, so there is NO LABOUR cost for the first hour.