I'm from Portugal, maybe some portuguese can help me since he's familiar with our bank cards system?
Most debit cards in Portugal that i am aware of are recognized as "Visa".
If yours doesnt have the number CVC code(think thats the name), you might try to creat a mbnet card by associating your bank acct with the service. It creates a temporary card with a code and card number and expiration date, all the needed stuff to buy online. If the shop also asks for more details like Name, adress etc, use the details of the bank account being used to create that mbnet card.