only given a 2.5% discount instad of 5% for delayed order

ordered 18000 plain t-shirts and 18 000 caps for ANC, all delivered for free to Cape Town. the order was 1 day late, the courier company they used could not give a proper explanation why the order was delayed. they promised a discount of 5% for the delay but up to now they only gave a 2.5% discount saying the delay was on from their end. we still need the other discount as promised.