What should I do about NCO Financial Systems? ?

I got a letter from NCO Financial stating that they would accept a lump sum settlement of less than my original debt. It sounds like a good deal, but after reading all the negative stories about NCO, I don't know what to do about this. My original debt was with Chase Visa. They said they were going to turn it over to a collection agency, but I don't know if I trust sending hundreds of dollars to NCO (whenever I get the money). The letter also asks me to call them before I make the payment to make sure the settlement offer hasn't expired. I want to call them to see if they can tell me exactly when the offer will expire, but if I do that, they'll have my phone number and bug me 24/7 like they've done everyone else. I also considered calling the credit card company and asking them about it, but they called nonstop every hour when they had my old phone number. I don't want them to start that again. I want to pay off this debt as soon as possible, but how do I know if these are the people I'm supposed to pay?