WOW. Sleaze is about the right word for it.

I'd kindly ask them to produce said voice recording of you authorizing any work above and beyond the initial treatment of your property. I'd tell them that if your differences cannot be resolved and they wish to pursue collections, that you'd be more then willing to contact the Attorney General in your state and see about filing a complaint.

Not that it helps a whole lot, but I've filed complaints with the BBB before too, but it didn't get me too far. BBB is more loyal to the businesses paying for accreditation then protecting the consumer. Angie's List is a good resource to use when trying to find a good contractor. This only helps in the future of course.

Hoping you get this resolved!!
Shannon