Are you sure that your SDXC card is not faulty? Before retrying, I would perform one or two tests on the card:
When there are no useful data on the card, format it (with a FAT32+an exFAT or NTFS file system) before use. Older cards sometimes have faulty file systems you can get rid of by re-formatting.
If this does not help (or itself creates error messages), I would use a testing tool like h2testw
to dind out what's wrong.