Review parcel pistin

hi and good day.
on Monday the 6/06 I posted a parcel, weighing 2.4kg according to the scale, containing books/documents. I thought the cost would be R99, as advertised. the assistant then started measuring the box, stating the size is big, I used a box that one buy the 5ltr water in.
the total amount came to R179.almost double as advertised.WHY wasn't this mentioned in your advert.and the invoice state a weight of 8.53kg
this is incorrect
I was served by Bradwin at postnet in Parow center
I a widow felt very disappointed at the charge rate, why arent they transparent in their advert.
regards
azeeza