Sorry to hear there is a bad apple in the Roto Router barrel. I have had good luck with the local franchise, and others here have given them good marks. Might let their national office know. One trick I learned from the locals is to pull off a stool to give you access to a 4'' drain. Before doing that, probe around outside near where you think the drain exits your house. You could happen on a clean out. The Rigid machine Tom says with a 4'' cutter might cut through the roots. At least it would give you a good measurement to start digging as Tom said.