So, they refused my pay for delete both by phone and by letter. I said to hell with it and paid in full after three attempts (last outstanding debt). My scorewatch had lapsed so I signed up again and got my credit report. 50 points higher (wooh!) and no sign of the charge off anywhere.
I did not GW or even enclose a letter, just sent in the full amount owed.
Don't know if that's standard practice for them, or if someone felt sorry for me, but my CO is now gone. I know others have struggled to get them to agree to anything. Maybe you just need to pay anyway lol?