All you have to do is send a CEASE AND DESIST letter to Halsted Financial. They have to comply. Send the letter certified and put the date on the letter, then sign it. Mail it and give it a week. Record EVERY call and take a photo of the caller ID. Mention that in the letter as well if need be!
Halsted generally buys old debt accounts that are past the statue of limitations for any legal actions. Generally the original creditor has written the account off as ZERO and Halstead purchases the account for less than pennies on the dollar.
Example, you have a debt that you didn't pay that was $200. Bc of late fees and other charges it is now $350. After a while, the original creditor will consider the account non collectible and will write the account off as $0.00 (They have ways to cover the lost). Companies like Halsted will then purchase the account for like $3.00 and collect on the full amount -$350- or more. It is practically a 3000% profit for Halsted. That's how they stay in business.
Either way, you are responsible for the debts you incur. However, in situations like these, where they are rude, use deceptive tactics, it is best to just write a cease and desist letter and make the calls from Halsted stop.
Unfortunately, the calls won't stop, generally another bottom feeder creditor will purchase your account and the cycle will resume.
For more information google FDCPA laws and FCC. There is a wealth of information out there to stop harassing phone calls and to settle accounts.