I am going to attempt to explain this again.
Debit Card = Available funds in a bank account.
Credit Card = Amount of credit available.
A Hold is a reserved amount that is placed on the account regardless if is a Debit or Credit Card.
5-8 Day Cruises is $200, they will increase this Hold if you go over the original hold with your account.
They do not "freeze" anyone's account. If you use a Debit card with a Bank Account with $350 in funds and they end with a $400 Hold then will not work untill the account is settled.
Let's say as a hypothetical I have $1500 available credit on a Credit Card. Carnival puts a Hold for $200, then increases to $400 when they see I am running up my tab. My Card would still work any where I went.
If someones Debit did not work after the Hold was placed it means they did not have enough funds available in their bank account to cover the Hold amount.