The interest that EBS have paid you seems about right.
Interest is calculated on a daily basis, based on the closing balance you have in the account that day. The interest is not added to the overall balance until the end of the year.
So for example if you opened the account with €1000, then each day after that you earned (0.05/365)*1000 or 13.7c per day. This continued everyday until you lodged another 1000. At that point your balance became 2000, so the daily interest went up to (0.05/365)*2000 or 27.4c per day. This continued on until a year later when you had 12000 in the account and you were earning €1.64 everyday.
The table below might show it a bit clearer. (Sorry about the formatting)
Month Days Balance Daily Interest Monthly Interest
31/08/2011 31 €1,000 €0.14 €4.25
30/09/2011 30 €2,000 €0.27 €8.22
31/10/2011 31 €3,000 €0.41 €12.74
30/11/2011 30 €4,000 €0.55 €16.44
31/12/2011 31 €5,000 €0.68 €21.23
31/01/2012 31 €6,000 €0.82 €25.48
29/02/2012 29 €7,000 €0.96 €27.81
31/03/2012 31 €8,000 €1.10 €33.97
30/04/2012 30 €9,000 €1.23 €36.99
31/05/2012 31 €10,000 €1.37 €42.47
30/06/2012 30 €11,000 €1.51 €45.21
31/07/2012 31 €12,000 €1.64 €50.96
Gross Interest €325.75
Net Interest after DIRT €228.03
The figures of 228 and 225 don't exactly match but that is because you have an extra 100 in the account somewhere.