Sd card not working properly

I purchased 16gb sandisk class 10 microSD…
but when I copying file into it… its not reading properly… sometimes Uuuuu.u file shows here…

and its mobile is notifying that please iinsert class10 sd card…
I’m confused, everything is oky of this card… symbol of class 10given there…

what to do now?

Return it to where you bought it as defective and get another one?