Is it within your states SOL? If this is fairly aged-at this point a paid charge off is going to cause more FICO damage, because it's going to show recent activity. You may have woken a 'sleeping giant' so to speak- they may turn it over to a collection agency of decide to file suit. It's up to you- do you feel a moral obligation to pay your debts? Sometimes you think your doing all the right things and it turns around to bite you- That happend to me when I disputed an old Crap! charge off... The thing now updates everymonth as charge off - while before I disputed it was showing OK for the past 3 years.
As far as sending a letter to the CRAs- they are going to report what SCANA tells them to.
Did you offer pay in full or a settlement amount?
What was the last reported/updated date?
While paying may not increase your score, paid vs unpaid looks much better to a future lender. Especially if you can explain why it went delinquent and explain that once you could you PIF.
I had something on my credit report for Scana for like $800 - one day it said charge off with a $0 balance. I emailed the customer service to see if I could get it removed since it would fall off in 2 or 3 years anyway. So I looked up an actual address and sent a GW letter to the head of the company. A week or two later I got a letter saying they would remove it.