Most of ATMs in Taiwan don't have fees for international withdrawals, including Visa / Mastercard.
However, some ATMs might make you pay a fee (usually NTD 100). So unless you're in a big hurry, cancel the transaction and find another ATM.
The 7-Eleven convenience stores ATMs will make you pay this fee, but the Family Mart ones won't.
Mui Ne is known as one of the most beautiful beach city in Vietnam. It takes 250km in 4 hrs transfer from Nha Trang. There are many interesting sight-seeing that you never want to missed: Long Beach, Salt Field, Bau Truc Pottery, Pink Sand Dunes, White Sand Dunes.