Back up what you can from the card, throw it in the bin, and buy a new one from somewhere reputable. You have been scammed, and there is nothing you can do to save the data.

In more detail: a very, very common scam with microSD cards is to take a cheap, small card, reprogram it so that it tells the device that it has a high capacity, repackage it and sell it as a high capacity card. The problem is that the phone thinks that the card has more space than it really has, so it keeps on writing after the card is full, and that results in data corruption (typically the newer data overwriting older data, but with the file table not matching reality nothing is safe). And this is why there's no realistic hope of recovering anything. Of course you could try putting it in a card reader and seeing whether file recovery software can get anything, but that stuff is designed to recover files where the file has been deleted but the data haven't been overwritten, so I doubt it will help with this.

Sometimes it's easy to spot these "fake" cards, e.g. if you see someone selling a 2TB microSD you know it's a scam because they don't exist, but most are hard to spot until you have the card in your hand and can run some tests (e.g. the h2testw utility, which fills the card with data then reads it back and checks for errors). Cards bought from online markets are a very high risk of being fake, so never buy a microSD card from eBay, Alibaba, Amazon marketplace sellers, etc. Occasionally these things get into legitimate supply lines, but in those cases you can at least get a refund: a traditional retailer or a major online retailer themselves cannot just shut up shop when they get complaints because it costs them too much, whereas a scammer selling through an online marketplace can just disappear or let the market close them down and then set up again under a new name (which is the usual MO).

The bottom line though is to be wary of cheap cards (the old maxim that if it looks too good to be true it probably is), don't buy cards from random web marketplace sellers (review scores are not a reliable indicator, they can buy those, or even get legitimate reviews from people who haven't yet encountered the problems), and if you have any doubt test the card before relying on it.

I'm sorry you are in this situation, but what you describe sounds like a textbook case of this particular scam, so I'm pretty much certain that's what's happened.

 

i would like to add to what @Hadron said.....and that is to use either smart switch to back up your photos and videos consistently and or use google photos. google photos backs your photos and videos to the cloud automatically. i never have to worry about my pictures or videos. i can get a new phone, signed in to google, and all of my previous photos and videos will be there.