What does op pakketzegel staat 2.60 en heeft 8.50 gerekeid mean in English?

Answer 1

'gerekeid' isn't a Dutch word. I'm assuming you mean 'gerekend'.

(quite literal) translation: The parcel postage stamp says 2.60 and has charged 8.50

(this sounds better to me):

The parcel postage stamp says 2.60, but it cost 8.50

Reading this sentence I'm assuming the post office has either overcharged (the stamp says 2.60, but they had to pay 8.50) or the package was heavier than the sender had expected and they had to pay more than the avarage parcel postage stamp costs.