For those that don't know what it is, it's a fabrication of a non-lawyer on the internet that claims that by failing to respond in an arbitrarily-defined timeframe, a collection agency is barred from collecting by estoppel. There is no timeframe dictated by the FDCPA and the letter is worthless.
There are some VERY effective ways to deal with these people and that ain't one of 'em.
That’s not what I was thinking about, maybe I meant Cease and Desist Letter.