Hi Mandya22,
I'm new to these GW/PFD letters, but I'll try to give you an answer based on my understanding. It sounds like the negative mark on your report is from Capital One, and not from Northland Group who now hold your debt. The Capital One collection will remain on your report as bad debt, and might also say closed since they've reassigned the debt elsewhere and now have nothing to do with it. If Northland Group now holds your debt, I don't think a PFD letter will work with them because they don't actually have a collection mark on your credit report to delete.
My suggestion would be to accept a settlement with Northland to close the account and save you money over the long run. You don't want to just stop paying it, because then that will probably also end up on your credit report. When you pay the settlement with them, send a cashier's check and send it by certified mail. That way you'll already have the funds taken out of your account at a time when you're prepared for it instead of them cashing a check months down the line, and they won't have your banks routing information from your personal check to possibly take even more out of your account (and trust me, the collection companies are that shady). Send it certified because the cashier's check is a lot like sending cash and you don't want anyone to be able to say it got lost or didn't get to them.
Then, send Capital One a letter asking for a Good Will Adjustment to your credit report. Explain your situation nicely and sincerely, and perhaps even mention that you've now paid off the debt that went to collections. Include any reciept from Northland Group, or a copy of the cashier's check as proof. I recently sent out several GW letters and a couple PFD letters. So far I've only heard back from the first GW letter I sent, but it worked and they agreed to delete two accounts from the credit bureaus! So it's all worth a try, and from what I hear keep being persistent if you don't initally get what you want.
Here's a link to the forum covering GW letters....
Good luck!