*****ulent deductions from account

I booked an international courier online. I specified that it was for documents A4 dimensions, 15 pages. My confirmation notifications and shipping label confirm the type of parcel. I was charged R783 for it. Then after a few days another R600+ was deducted from my account. I have spent over a week querying the second deduction but UPS (Sibonelo James Kumalo) refuses to refund me saying that they estimated the parcel to be 0.5kg but round it off to 1kg.