If it doesn't have any brand on it, it might be defective. Try formatting to FAT32, and if that doesn't work then it's not going to (probably). If you have a PC, you'll need a program called 32formattergui, or something like that.
Curious, why not use SDFormatter? Considering that program was made by the association that developed the SD card standard, after all.
That's also one reason I was abhorrent to picking up a 128GB microSD for my Gateway-3DS's red cart. At the time, it would have been the only thing I could have used it in. At least now, I also can use it in my current phone. Though personally, if the 3DS portion of the DStwo Plus would have worked as advertised, I would have easily filled up a 128GB microSD on that setup.