Sorry to hear my friend. I hope you have better luck with the second one!Still no success.
The guy at the store didn't know how to solder correctly, and after 3 attempts, he gave up and gave me back the two emmcs (the 256GB and the original 64GB) and the empty motherboard
I ended up having to buy a heat gun and try the soldering myself.
After many soldering attempts, I ended up getting it working for a day, but the next day the emmc died. the cause of this may have been the excessive attempts I made (the heat may have deteriorated the IC).
I ended up buying a second emmc but it should still arrive next week