Best steps to take when contractor overcharges for materials

[Christopher M Miller]

My wife and I have a rental property in San Antonio, Texas (Go Spurs Go!!!).  We've had a new tenant move in and hired a contractor remotely (we live on the East Coast) to mend to a few issues.  The previous tenant did not fill the water softener before leaving, so we had to hire for that.  

Once we got the invoice for services performed, we were charged 20.00 per per one 40 lbs bag of water softener pellets, for a total of three bags for 60 dollars.  Typically those bags retail for around 7 dollars.  We were also charged separately for labor.  

My wife wanted to fire off an angry email, however I told her to wait for 24 hours an ask what others have done when being overcharged by contractors for remote work.

thanks