Possible gas scam?

To sort of bring this to a “happy ending”, on recommendation I had Ambifuego come to check the set up. I had three calls confirming the names of the fitters, and confirming the timings. They came at the appointed time, checked it out and yes, I do need the work to be done, but at a fraction of the cost and there was no danger in us using the oven at all! Live and learn eh? Thanks for all the advice though, much appreciated.