I am NOT a lawyer, but unfortunately have a pretty good understanding of this kind of thing. There are many ways these characters violate what is called the FDCPA (Fair Debt Collection Practices Act).
For example:
The hours that are LEGAL for any debt collector to call are 8 a.m. to 9 p.m 7 days a week. They may not cause your phone to ring "excessively." They must send you a "Dunning Letter" identifying themselves as a collector within 5 days of the first call.
Only some of the FDCPA applies to the original creditor. The real slimeballs are usually the 3rd party collectors anyway.
Get to know the basics of the FDCPA (Google it). If collectors are in violation, you can find law firms who will sue them. You could be awarded up to $1,000 and the collector pays the legal fees. Beware that there are rules you must play by as well. Even if you win, if you actually owe the money, there could still be consequences for you.