This happened to me. Once your card is blocked, no one including you, can use it. It would be possible that someone used your card information online or in person if they did it before the bank blocked your account. When I told my bank about my missing card, they told me to go to the bank's online site and check for any unauthorized charges, since all charges are posted there immediately. I told them of two charges that weren't mine and they deleted those transactions.
BTW, when you get your new card number make sure you change any direct debits that use your card number, and change your card number on frequently used websites, such as PayPal, Amazon, iTunes, etc. If you forget to change to the new number and try to buy something you will get an email or phone call saying the transaction can't go through until you give them another card number. But don't count on them reminding you, because I had an account go three months past due because I forgot to change the payment information and they never told me there was a problem. So keep a list of all accounts tied to your card number just in case, because a month after having my stolen card replaced, the bank was hacked and they forced me to get yet another new card and I had to inform everyone once again.
From what I understand with online banking, you have a username and password that you use in order to log in and unless the person that got hold of your card (if anyone did) knew your username, password, date of birth, etc, than no, they can't use your account online. It's a severe impossibility.
I won't matter if someone tries to use your missing card as the bank will have blocked it straightaway. The new card will have changed numbers.
No. That is what blocking the card does, it stops people using it.
When your new card is issued it will have a different account number and the old account number will have been deactivated and no longer usable.
Yes
if it has been cancelled, it won't work anywhere - relax
