Mr. Rooter Plumbing of GTA

I called Mr. Rooter Plumbing and ask if I can get a quote and got informed its free to get an estimate. On that day I was called by my tenant that the bill is $750. I was shocked and then called the company ask why just replace the mixing valve it will cost such huge amount of money. I asked what labour rate they have and what is the cost for the valve. Company manager advised I will get a call back but then I received this invoice and tenant told me the job is done already. I called the company again and was told they will give me a discount makes the price to $542. I said but this job is done without my authorization. I called the agency confirmed he did not authorized the job too. Since my tenant already paid them. I called them ask if we can lower the price to $300. They said no. $300 was according to one of the plumber that work for my friend's house. Usually the labour rate is $60-$65/hr, and the valve as per the pictures cost $110 - $230. I dont think the price is reasonable and they just tell me that's just the price for everyone that replace the valve. And they always use the same valve.