The chocolate giant has also changed the recipe, and customers say they now taste "revolting".
Single packs of Snack! shortcakes still have an RRP of 55p but Cadbury has taken two biscuits out of the pack.
The firm – which is owned by US multinational Mondelez – said that it has made the remaining biscuits in the single packs bigger like the ones in its multipack of six two-biscuit packs.
Cadbury explained that it wanted to reduce the number of calories to under 200 in single packs "to help people enjoy their favourite treat in a satisfying, portion-controlled size".
But fans are furious at the change – and they've also noticed that the recipe is different too.