SanDisk Extreme SDHC 16 GB Memory Card up to 60MB/s, Class 10, U3 faulty possible fakes?

I brought a twin pack of these and both failed when the became locked and having contacted sandisk they asked for a serial number from the back of the card which there wasn`t ,Amazon have refunded me the money and today i brought another sandisk card from tesco and this also had no serial number on it can anyone tell me if it caould be a fake?

Test it with h2testw.

It is strange that are 60 MB/s and not 90MB/s, if you want to upload a photo of the front and back, The serial number must be on the back side.