Very old collection account refused certified mail. Porfolio Recovery

Hello Bo, I have an account on my report that is very old. Over 12 years. Anyway, I sent a validation letter - certified mail to the collection agency, Portfolio Recovery. All they did was refuse the letter. What is your suggestion? Should I keep sending until they accept or just dispute with the bureaus? Thanks for any help you can give.
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did they refuse the letter
or did you get the wrong address
or was it sent to a po box and they are asked to sign.
doesn't make sense for them to refuse it

try certified delivery only.
I'm not sure whart the name is when the have to sign but it is not certified delivery.
that way the post office certifys they delivered the mail.
no one has to sign for it
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NEW QUESTION
I had my credit run by a mortgage company recently and on the report it listed the addresses as: equifax po box 105873 atlanta, GA 30348
transunion as 2 baldwin place, in front of the po boxof 1000 chester PA 19022 ( strange)
the experian as Po box 2002 Allen tx 75013
I am not sure which address to send my letters???
I guess I can call to confirm the addresses.
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no
use these
www.oskie.com/credit-dispute.htm
they work
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ok, i was just wondering why my credit report had different addy's. but thanks, I will. I decided to take care of it myself. I had two mort. referrals who wanted to charge me between 500 and 1750 to remove.... sha right
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the addresses on reports usually are for creditors not consumers
these work

good idea on doing it yourself.