There are many fake microsd, so you might got fake sandisk microsd.
The problem is with SanDisk is they have / had many different lines / price points of SD cards
a quick search of 64GB from Amazon:
Ultra $ 10.99
Extreme: 14.99
High Endurance: $13.49
Extreme Pro $25.95
Extreme Plus $12.99
You then have to spend some time searching about which ones have which features.
And then they did (might still do not sure since WD took them over) have some slightly different ones that were sold at some retail spots.
Going back to my car example it's like saying you bought a small Honda so you could drive to work. You can get a $17000 Fit or a $36000 Civic Type R.
And then you have to worry about the knockoffs.
As for the get a real computer comment. There is a point. If you want it done quick and simple getting a used PC can you up and running (possibly for less money) if you want to learn and play and tinker, getting the RPi is good. If you want to get to work get the Honda Fit, if you want to get to work with tires smoking while sliding through corners and engine screaming get the Civic Type R
-Dave