I was watching a show the other day where a financial advisor comes in and does a “money makeover” on people who are deeply in debt. One of the first thing she did was freeze their credit cards into a block of ice, so they couldn’t use them. Which got me wondering, would the cards be “scannable” after thawing, or would the magnetic strip somehow be damaged from the ice or temperature?
They may work better. One last resort trick for hard drives that are failing is to put them in the freezer for a while and then quickly connect them to move data. I don’t know how but I discovered that same trick with my 5 1/4 floppy disks for my Commodore 64 and it works. Credit cards are pretty resilient. I sit in mine all day in my back pocket (in my wallet) and they seem to work fine. I have washed them and gotten them sweaty as well with no known damage. It doesn’t seem very risky and you can always call your credit card company to say yours isn’t working right and you need another one. They will send you one in a few days which doesn’t seem much of a problem for this purpose.
Different mechanism in the case of salvaging the disk. The reason it might work is that the disk is probably suffering mechanical failure, and warping the disk geometry by freezing the thing might temporarily correct it - or make it worse. But if the disk is dead already, you may have nothing to lose, beyond possibly making the situation worse if you are going to be willing to shell out the bucks to have a data recovery business recover the data for you (probably about $1000 - $2000).
The point of freezing credit cards in a block of ice is that you have to wait a while for the block of ice to melt before you can use the card. Since many purchases are ‘impulse buys’, the hope is that during the time it takes for the ice to melt, the buyer will have time to realize that they don’t really need this item, or that they can’t afford it, and so won’t make the purchase.
It may be more a psychological trick than anything, since many purchases are done over the phone or online, where you don’t need the physical card, just the number. And with microwaves or boiling water, it really doesn’t take that long to melt a block of ice anyway, if you are really determined. The block of ice is set up as a mental barrier to remind you not to buy on credit.
But both of these would definitely render the card unusable, if the freezing didn’t.
I can tell you from personal experience that freezing a credit card into a block of ice will not harm the magnetic strip. Neither will running said block of ice under hot tap water to defrost it. 
I’d believe microwaves; I’d want a cite for limited application of boiling water rendering a card unusable. (Note I said limited - we’re talking a credit-card-addict rescuing their cards from a block of ice here).
I’d expect that freezing would be just fine. It’s heating that causes magnetisation to fade.