Default MicroSD card help

Hi everyone,
I have a 64gb sandisk microsd external card, in a att galaxy s3 and it appears to be acting very strange.
i can't add or delete anything from it, i put it in my brothers galaxy s2 to format it (my s3 not having the option(which is strange)) and it let me format it, but when it remounts its at the exact same place, with 42.2gb free storage space, which is what it was at before i formatted it, i did it a few times same thing.
if i manually try to delete things from the card through my phone or computer they either hang or they do delete then upon reboot all the files are back. I hope its not corrupted but it sounds like it is. i've used a few apps like sd tools which runs speed tests, and i get about 130mb write speed a second and 5000mb read speed a second which sounds like it should be able to read and write things but unfortunately it just won't
any help would be greatly appreciated.