They may have taken over responsibility for something in 2004 that relates to a previous credit provider.
I found this if its any help:
https://www.santander.co.uk/personal/support/customer-support/ppiProviders Santander are responsible for investigating
To make sure the correct provider will investigate your PPI complaint, here are the providers Santander is responsible for investigating regarding PPI claims.
Abbey
Abbey National
Alliance and Leicester
cahoot
Cater Allen
First National Motor Finance
First National Wagon Finance
HBOS (Unsecured Personal Loans)
JP Morgan Classic Deferred Debit
National & Provincial
Santander
Santander Credit Cards
Store Cards:
ASDA
B&Q
Bentalls
BHS
Boundary Mills
Budget Tyres
Burton
Care+
Comet
Country Casuals
Currys/Dixons
Debenhams
Dickens
Dorothy Perkins
Edge
Ernest Jones
ETAM
Evans
First National
Trust Finance
Flemings
GE
Goldsmiths
High and Mighty
H Samuel
Halfords
Harrods
Harvey Nichols
Hawkshead
House of Fraser
IONICS
Kwikfit Finance
Laura Ashley
Leslie Davis
Lombard Tricity
Finance
Matalan
Miss Selfridge
Monsoon
Mothercare
New Look
Outfit Card
Owen Owen
PayPal
Power House
Principles
QVC
Racing Green
Reids
River Island
Russell &
Bromley
Ryanair
Signet
Time Retail
Finance
Top Man
Top Shop
Toys "R" Us
Uptons
Value Direct
Wade Smith
Wallis