Microsd Sandisk Ex Pro 16gb Cannot Save Anything

Hello, I just bought microSD extreme pro 16gb for my phone. However I am unable to write anything on this card from the cell pone or through the PC. I have tried formatting the card but I get the message, “unable to format card”. I try to copy several files and successful, but everytime i disconnect it from pc or my phone (unmount) and try to connect  (mount) it , all files gone from card (the card is empty, like someone has just formatted it). Anyone can help? 

Return it. it’s defective.