Sounds like a tree removal service would be your best choice. They would be expensive but would be worth it just from the stand point that if something goes wrong their insurance should cover it. Make very sure on that point. Your plumber should be able to recommend a good one
If you don't like that idea, there should be a free service to mark the utilities. After that a lot of digging, a lot of root cutting and a lot of sweating should get it out.
BTW, although the city (around here) gets a lot of blame for things like lot layout and street layout in any given developement, that is actually done by the developer or someone he hires and in a few cases they wern't very good at what they were doing. In the case of one road the story is that they were drunk when they laid it out.
