I got a counterfeit card from ebay once. It said it was 64GiB, but writing anything past 32GiB resulted in file corruption. Likely it was a 32 GiB card with allocation mapped twice to look like 64GiB. Writing past 32G was probably remapped to the beginning and overwriting the existing files. A PayPal dispute got me my money back.
This doesn't sound like your issue though. More likely, your card has been partitioned. An advanced disk management tool should be able to make a single partition, then it can be reformatted. I don't know of a Windows tool for this; I'd use gparted for linux since I don't do windows if I can help it.