Yup. My 64gb Ultra micro SD card is dead as well. Write only. Old content can be read but deleting/formatting does nothing. Really disappointed to have 2 Sandisk products fail on me this year.Also, trying to RMA a storage product with personal files on it is a no-go for me. Ridiculous situation that I will avoid by not purchasing a Sandisk card for a replacement.
contact sandisk support. they have a process for returning cards with sensitive data on them. they will be happy to work it out for you.
The article windows was unable to complete the format may help you!