That is because only about $12-15 each month are going to the principal. When you look at the balance just before you pay again, the interest brings it up to above that so when your payment comes in, once again it only lowers it about $12....
You are getting a settlement offer now because they are financially in trouble again. You can either wait until they sell of your account or just get it paid and done and over with. Personally if I had the money I'd just get it done and over with, but I can't even afford the $140 something a month they are offering me.... and the 47% would be nice, but just can't give them anything right now.....
You could wait it out and see if they'll lower it anymore....but they might just sell it. Which then that'd go on your credit report.
And anything you agree to, if you send them money have proof that the money is supposed to do what they said it would... Get a document, anything in writing....