We understand your feelings, so to avoid any misunderstanding, let's check how this feature works.
The thing is that to get the fifth package for free: you should make the SAME four purchases through the Buy Menu or the pop-up “Not enough coins.”
All purchases which were made in special offers, Coupon Climb and sales are not related to this feature.
Despite not getting you closer to the fifth pack, such purchases give you a huge benefit in collecting special offers rewards there are extremely profitable.
In any case, we're always here to assist you, so if you still have any doubts, contact us via the Support button, and we'll make the situation crystal clear.