You own the house, you own the problem.
Have the roots cutout, or live in sewage. Your choice. Not sure why you did not have roto rooter do the cleanout while they were there. That is a common pipe cleanout problem if you have trees.
As far as the scare tactics are concerned, never deal with anyone who trys to rip you off that way. Get a price from a few other people if you want to make a big deal out of it. You want your pipes roto rootered, not your pocket book.
I would just have the roots roto rootered when (and if) the pipe clogs up again.