If you take your card to Macau you have to add the extra digits, so I discovered once the hard way.
Cards get demagnitized all the time. I have had some for years, and some that need replacing every few months. It happens.
If you really want to protect your card, you can consider keeping it inside a sleeve (I get this nice packing paper wove grade sleeves with my cards when the bank sends them to me). I just keep the sleeve in the wallet and pull it out when needed.
Some people say certain types of wallets aid in demagnatism, but I think it's kind of an urban legend. Throwing you wallet on top of a spinning hard disk in a laptop or a computer won't help things, nor will leaving it around other things that may create a magnetic field.
You may want to check if you need to do some '00' thing but I think the easiest is just to break the thing and take it back. Just chip a corner or something using it to cut something.