[Q] can't delete some files and folder

Hello, i'll try to explain what's my problem in the best way... sorry for my english...
I used Airdroid to transfer 2 songs downloaded from iTunes from pc to my Vodafone Galaxy S3. I save those 2 songs in sdcard0/mnt/extSdCard/media (now Airdroid can't see sdcard with Android 4.1.2) and than i move in extsdcard but songs in sdcard0/mnt/extSdCard/media still exist so i try to delete manually in a lot of way but i can't.
If i copy this files in sdcard0, but in other folders inside sdcard0, i am able to delete files but not in sdcard0/mnt/extSdCard/media.
I've create a New folder in mnt/extSdCard and also this folder now it's impossible to erase.
I've try with stock file manager, with x-plore and also from pc but nothing.
I would like to delete this files without wipe and root, i think it's an app that cause this little but very annoying problem.
I hope someone of you can help me.
Have a nice week end.