Over charged

Got the guys from drainsure to detact a leak in my house. They gave me a quotation and I decided to pay them the full amount. After leak detecting, they had to come and fix the leak. Received two invoice for leak detecting and repairs, instead of the company subtracting the amount I had paid and only charge me the balance for repairs they over charged with an amount of R685. Since the beginning of May, I have tried many times making a follow up on my refund but everyone at the company ignores my emails. Spoke to Marietjie, whom now has left the company. Spoke to Shaun who said his partner Werner would be making payment into my account. It is now the 1st of July and I am still waiting.