I just finished dealing with them, and if you have to, my advice is to do ALL your dealings with them in writing. I sent a DV letter, they responded quickly, and also responded quickly to my payment plan request. I sent them two payments for about $600 less than the debt owed, and they did send me a debt payoff letter when everything was paid off in full.
If you get the initial letter from them, DON'T call, just send your DV letter first via either certified mail or priority with delivery confirmation. In your letter tell them not to call you. They complied with my request, and the whole experience was pretty tolerable, which is something I never thought I'd say about a debt collector.