PPI store cards - Santander

In November I made a few calls to find out if I had PPI on any of my store cards in the late 1990's/early 2000's and was surprised to hear that 4 of my store card did! Santander said they would look into the 4 together for me and sent me a form to fill in regarding my situation at the time.
I filled in the form basically explaining that I had no idea that these cards has PPI on them and that I was a full time student at the time only working p/t in bars. The form requested employers details, I entered a few bars I worked in - baring in mind this information was not specific to 1 but 4 cards. Santander have since written back to me to say that they do not believe that they should uphold my complaint for 2 of the cards. Stating "However, you've indicated that you were previously working less than 16 hours per week. In addition, you've indicated that you had more than one job at the time the policy was taken out. In addition you've indicated that you were a student at the time the policy was taken out." I'm really not sure what they are getting at here - any ideas?
They now want me to fill in a form with more specific questions relating to my university course, part time work hours, employer, start and end dates with evidence!! Now this baffles me as they want me to be specific and answer all these questions but for TWO cards taken out a different times. Also I can't remember definite dates, times as it was casual bar work. Can anyone advise what I should do now? Thanks