What the caller actually bought explains most of what happens next. After an account is charged off, a creditor either refers it to an agency for a commission or sells the file outright. A buyer that purchases a portfolio receives account data rather than the underlying paperwork, and the further a file travels the thinner that data tends to be. This is not a moral observation; it is the practical reason a specific written dispute so often produces either the documentation or silence, and why a balance can reappear months later from a different company entirely.
The dispute right is more powerful than its reputation, and the 30-day window is not what people think it is. Under 15 USC 1692g(b), if a consumer disputes the debt in writing within 30 days of receiving the validation notice, the collector "shall cease collection of the debt ... until the debt collector obtains verification of the debt" and mails a copy to the consumer. The same subsection is explicit that collection may otherwise continue during those 30 days, so the deadline is not a deadline to dispute at all: it is the deadline to get the automatic stop. It also requires that anything the collector does in the period "may not overshadow or be inconsistent with" the disclosure of the dispute right. And 1692g(c) removes a fear that keeps people silent: failing to dispute "may not be construed by any court as an admission of liability".
A written instruction to stop contacting you is a separate right and it binds. Under 15 USC 1692c(c), once a consumer notifies a collector in writing that they refuse to pay or want contact to cease, the collector may communicate only to say its efforts are ending, or to notify the consumer that it or the creditor may or intends to invoke a specified remedy. Two things it does not do, and both matter: it does not cancel the debt, and it does not stop a lawsuit. Sending it to a collector who was about to sue simply removes the letters.
The contact rules are more specific than the phone calls suggest. A collector may not communicate at an unusual or known-inconvenient time or place, and absent knowledge to the contrary must assume that convenient means after 8am and before 9pm in the consumer's own time zone. It may not contact a consumer it knows is represented by an attorney about that debt. It may not contact a consumer at work if it knows or has reason to know the employer prohibits it. And under 1692c(b) it generally may not discuss the debt with anyone other than the consumer, their attorney, a credit bureau, the creditor and the two sides' lawyers. Calling a relative to ask where you live is permitted only under the separate location-information rules, which forbid stating that the consumer owes any debt.
Regulation F added the media rules, and they are unusually specific. Under 12 CFR 1006.22(f) a collector must not communicate about a debt by postcard, must not put language or symbols on an envelope that reveal the business it is in, must not email an address it knows the consumer's employer provided, and must not communicate through a social media platform "if the communication or attempt to communicate is viewable by the general public or the person's social media contacts". Separately, 1006.22(b) prohibits collecting any amount "unless such amount is expressly authorized by the agreement creating the debt or permitted by law", which reaches added interest and fees as well as the principal.
The Act is enforced largely by consumers suing. 15 USC 1692k makes a non-complying collector liable for actual damages, plus additional damages a court may allow up to $1,000 in an individual action, plus costs and a reasonable attorney's fee. Fee shifting is what makes a case viable when the measurable loss is small, and it is the reason documenting dates and keeping voicemails is worth the effort.