Ripping clients off

I called Homefires 26th of January as they were the installers of our gas line, at our new home ! I explained exactely what the problem is when we switch on the stove we smell gas and all the burners light at the same time, I also explained that we have 2 exact same stoves in our house and they are both doing the same! The lady said she has to send somebody out to come and have a look and that they would be there the on the 27th after 2pm, but I needed to pay R650 for the callout which I did. I got a call from Hanri at about 14h30 advising me that they need to replace the regulator and that his office will call me to schedule a time! I said but don't you keep them in your truck in order for you to replace it, no they don't !!! I phoned 2 other suppliers explained to them the problem and both said that the regulator needs to be replaced, why did Homefires first have to send somebody to have a look ? it seems to be a common problem and when they do send somebody they have no parts to replace the broken one? is this the way they make their money send somebody out charge R650 and then send them again for another R650 plus labour? I would never recommend or use them ever again!