I made a mistake printing a label and have been incorrectly chared shipping fee of $6.95

[stahlschmidt0]

I tried to print an address lable only and ended up being charged:

231180876601

22-Mar-14 18:07:28 AEDST

Australia Post shipping fee

AU $6.95

I used my own Australia Post prepaid postage bag to ship the item.

How can my invoice be adjusted to remove an item i did not use or require?