DP, how OLD is this debt???
I hate to say this, but you may have woken the proverbial sleeping giant. Now, they may go ahead and sue you if you don't make an arrangement with them. Depending on your state's SoL, you may have reset the clock.
IMO, NEVER negotiate a PFD unless it's out of SoL ... it gives them more incentive to accept the PFD. Otherwise, if you're still in SoL they don't have to accept it. They can shrug and just take you to court.
And FTR, I've never heard of Cap One accepting PFDs.
Give us your state and the date of last activity (last payment) AND date of final delinquency. We can then see what your options are.