I can certainly sympathize with you.
I think that you understand that the gas company is not your adversary in this matter.
It seems that they have been there a long time, and they are not the villain in the case.
The easement could be recorded; very likely it is. It was possibly granted by the farmer who owned the land a hundred years or so ago.
At closing, it would be the responsibility of the Title Company to document and record the existence of the easement. That's what we pay them to do. If you paid then to do that, and they failed to find it, you should get an attorney not affiliated with the title insurance company to represent and start the questioning.
Your attorney will know what to do with the developer.

