Portfolio Recovery ociates?

I got a letter in the mail today from Portfolio Recovery ociates concerning a credit card debt that is extremely old. It's basically giving me 3 options for paying back a balance of $1,965.47. My issue is this. While I don't know exactly how old the debt is, I recently browsed my credit reports with all 3 bureaus and nothing shows up as a negative. There is nothing referring to this debt or any debt in this amount on my CR. After having researched what I could on Portfolio Recovery ociates, it seems they have a bad reputation for pulling crap like this. I know the SOL for my state (PA) is 4 years and without a doubt I haven't paid them or anyone towards this account within that time. While, moralistically, I would like to pay this off, I don't know if I can trust them. I now know that nothing of this is showing up on my credit report which means that it's at least 7 years old, correct? Also, if I do pay off what they're offering, won't it STILL reappear on my report as a paid off collections? I know it sounds awful to say, but at that point what sense does it make to pay it? I want to do the right thing, but it seems they set it up to get their money AND screw you over as well. What type of letter(s), if any, should I send them? Cease and desist? Validation of debt? Anything else? Just looking for suggestions on how to go about handling this. I just received it in the mail today and haven't heard from or received anything from them prior. Help?