Note that I am not licensed to practice in your state.
Collection Agencies are ruthless. Their job is to get their money in any way possible and that includes all the things you mentioned above. Go online and google 'Fair Debt Collection Practices Act". It is the federal law that regulates how collection agencies behave and what they can and cannot do. It's a long list that you might want to keep handy just incase they violate any of the provisions (which is common). If they do violate a provision of it, you write them a certified letter and tell them that they cannot contact you any further because of the Act.