Slamming down the phone is the wrong response.
From 15 USC 1692:
(c) Ceasing communication
If a consumer notifies a debt collector in writing that the consumer refuses to pay a debt or that the consumer wishes the debt collector to cease further communication with the consumer, the debt collector shall not communicate further with the consumer with respect to such debt, except
If such notice from the consumer is made by mail, notification shall be complete upon receipt.
(The term "invoke specified remedies" refers to any actions ordinarily invoked by the bill collection agencies or creditors. Choices range from dropping, closing, selling, returning or transferring the account and can include seeking a court-ordered judgment.)
This doesn't excuse your debt! It simply stops the harassment. It also stops the harassment of neighbors, relatives, and co-workers. They are already treading on dangerous ground by doing this, because it's bordering on disclosure of information to a third party.
The call center may be in Pakistan, but it's being run by a US company. It doesn't excuse them from complying with the Fair Debt Collection Practices Act.
That’s very good information... thanks.
It certainly never stop them in the past. In practice they have no money to spare to fight it and a Jury will not be sympathetic. Its like breaking the law and then accuse the accuser of breaking another law.