Starting June 28th, you will no longer be able to log in to a Curse account that was not merged with a Twitch account. If you have not yet merged your Curse account with a Twitch account, please do so here! Otherwise, your account and its content will be inaccessible.
There is a link floating around somewhere. Have you checked your bnet account? Some people (including myself <3) have the option to download the Starter Edition. It's basically the beta version of the game but all you have to do is add a key to it and it unlocks the whole thing to move past level 13 and go beyond the skeleton king.
Note - This just downloads the installer for d3. You still have to actually install the game on the 14th.