So problem with Diablo 3 ofc...

I have read all the topics i could find and tried all solutions i could find and i am still stuck. so follows my story:

I cannot instal cus of error saying that i have dmg discs. solution is to redownload that 50mb file that i all ready did but somehow still have .part file in my folder( i wated till launcher closed it self and said its all ok). so i tired again. and then occured another problem. when checking reaches the end is says Unauthorised download.

any solution?