FTR, a debt collector CANNOT tell a third party that he/she is a debt collector, and therefore MUST simply play word games with a person on the phone that tend to annoy most sane people.
We (as in my former colleagues and myself) know that you know we are collectors. We also can’t tell you on the phone that we can’t tell you who we are. :rolleyes:
This is also part of the Fair Debt Collection Act. Most states require that collectors take a class and learn the laws applicable to their states.
Trust me, though the collector may not want to believe you aren’t the person they are looking for, they would much rather find and talk to that person than yourself. Debt collectors work on a commission of sorts, and spending time and money talking to someone that doesn’t owe them any money is not only stupid, it’s counterproductive.
THAT being said…this business does attrach some real assholes. OR, assholes are made from being forced to hear 99 excuses an hour about why you bounced a check to the local supermarket.
If you did something to piss off a collector, some are not above calling you for pure harrassment. Ill advised, but it happens.
Write a letter, not email and have it certified. Send it to the agency, explaining that Collector X contacted you on X, X, and X days and you explained to Mr. X that you are not the person they are seeking. (Provide some MINOR evidence to this fact). Also state in the letter that the agency is NOT to contact you regarding this matter further. (Calling does NOT have the proper effect, as people can just claim they never actually got that call. A certified letter, signed for, is great proof for a judge.)
They WILL stop, and if they don’t (assuming, as you’ve said, you don’t owe them anything), then you can sue the collector who contacts you, as well as the agency for $10,000 per law broken.
(Aside from my overall honesty and sympathy for my fellow human being, the $10,000 personal fine kept people who owed me money VERY safe.)
I’m beginning to think I should start a “Ask the Bill collector” thread. 
~J