Wrong forum Under Payment Since 2006

I have just discovered that I have been under paid in my salary for the last 5 years. In brief I work (job share) form 8.30 till 5.30 but am only paid from 9am. Each Decmeber I receive a payment of € 500.00 which is to cover this extra time. It was done this way as to not effect our hoilday entitlement. Due to some other issues I actually worked out what I should get if I was paid for the half hour each day and it comes to € 883. per year. I have asked for this too be looked at for future payments, but what I would like to know is can I look for this to be adjusted back to 2006 or is it too late ?? The same applies to the girl that I job share with. Many Thanks.