ShockMe77, I feel your pain.....
I once "hole-sawed" a 2 1/2" section out of a 1" galvy gas line. I was on a remodel site, it was loud, and I did check under where I was drilling. However I didnt check good enough, (used my hand instead of getting under there and looking) and didn't hear the hissing, or smell gas until I removed the 'plug' I made with hole saw. At which point it was a whooshing noise and potent gas smell with a 2 1/2 " gap in the pipe. I was fortunate there was a plumber on site, and got it back together after several hours and a hefty change order / back charge. Things happen, lessons are learned....
I'm just gonna re-emphasize what others have said.
Most plasic gas lines have a "Ground" wire, usually a yellow insulated #8 solid run with them, (I think it is in thier codes to do so? I believe the pipe is to be yellow too?) and you can tone it out yourself. Utility companies wont mark past their meter, or entrance to the property. So in this case you just you are left to either hire out someone to trace it, or do it in house if you have the equipment, or rent it. But when it comes to plastic water, or irrigation lines your are screwed. So when in doubt - Hand dig.... Or better yet, "Trenching by Others" located on the contract in bold print.
I would have called a 24 hour service company to get thier butts out there on the spot, sometimes you cant be stingy.