Techrepublic bookstore shipping charges

So I ordered some books from the clearance. I paid $25 for shipping to Canada. When I get the package, I get dinged with another $15 charge by my postal outlet??

Talked to customer support, they say, well its your postal service that is making the charge.

My question is why the double charge? I already paid a shipping charge. The stance that Techrepublic is taking is that it is ok to get double charged if you mail a letter from Toronto to new York. So basically when Canada Post hands over the letter to US Postal Service; US postal service has the right to say, pay another $1 or else. WTF!