Send a cease-and-desist letter under FDCPA § 1692c to legally stop all collector communications.
Under FDCPA, collectors cannot call before 8am or after 9pm, call your workplace if told not to, contact third parties about your debt, use abusive language, or threaten actions they don't intend to take.
Before sending a cease-and-desist, log each call with date, time, phone number, and what was said. This record is evidence if you need to sue for FDCPA violations later.
Your letter needs only one thing: a clear statement invoking your right under 15 USC § 1692c to cease all communication. Send it via certified mail with return receipt to the exact name and address on the collector's correspondence.
Once they receive your letter, collectors may only contact you to confirm they will stop, or to notify you of specific action like a lawsuit. If they call again, each call is an FDCPA violation worth up to $1,000.
Log any contacts after your cease-and-desist was received. If violations occur, you can sue in federal court within one year for $1,000 per violation plus actual damages and attorney fees.