Send an
Subject Access Request to 02 which will give you details of the debt and what charges
have been added over the years [some may well be unlawful and therefore
reclaimable]. You should also find from the documents you receive if 02 have sold on the debt and from that you will see if the
debt collector has added
theri own charges [they shouldn't have].
Write and tell the
DCA what you are doing as you do not agree the debt figure, and for them to accept the letter as a notice of dispute, which prevents any further action from being taken until the dispute is settled.