They call constantly, and have even started bothering family members, some who live in different states. They do not acknowledge their responsibilities under the FTC rules, and, if you are of a mind to do so, report them. When they call, immediately tell them that you are recording the call, and insist that they provide the time, date, their employee ID number, the reason for the call, who they are trying to reach, the specifics of the account that they believe is in default. Do NOT provide them any information, just insist that they give that information to you. Call blocking is also effective.
More devilish, but an awful lot of fun if you have auto redial is to call them hundreds of times per day. Don't talk to them, just call them. Even more fun, if you have call waiting, is to call them twice from different lines. On the second line, when it prompts you to "press 1 for English", do so. That will synchronize the calls. After just about 1 minute, there will be another prompt asking if you live in New York City or one of its boroughs. Again, press "1". This speeds up the answering process. You now will have two confused people on the line, each asking each other for the other's credit card number. Occasionally they have fun with the process: "Hey, girlfriend! I guess we got our lines crossed." Sometimes they get annoyed with each other, and they always blame their IT department. If enough people keep their lines busy during the day, they might someday get the idea. They are a regulated industry, and continue to break the law on a continuous basis. If a lawyer reads this and decides for a nice class action lawsuit, I would be there would be lots of participants.