There are quite a few support articles on this starting here https://us.battle.net/support/en/article/compromised-diablo-iii-account
You need to:
1. Clean the malware off your PC (likely way you got hacked)
2. Regain access to, and control of, your account
3. Request an account restoration/rollback (keep the restrictions in mind that are in the arcticle I linked.To remove Malware:
1. Download, install, and update Malwarebytes (free version is fine). Boot into safe mode and run a FULL (not quick version) scan with the game up and gibberish in the login fields. Some malware only activates under those conditions.
2. When that scan is done, run a FULL virus scan with an updated virus scanner. Microsoft Security Essentials is free and decent these days. Some folks here also like Avast. Better than Nortons, MacAffee, etc.
3. From a PC you know to be free of malware, change your email password. Check it for forwarding as well. Sometimes hackers set up forwarding. To regain account access:
Submit an account recovery form https://us.battle.net/account/support/account-recovery.html
Do this ONLY after the PC is clean or they will just get more info about you.Secure your battle.net account
1. Change your bnet password again now that the PC is clean.
2. Create a new email that you use ONLY for battle.net and switch to it. Gmail is great because you can put two factor authentication on it and prevent hackers from logging in without a code.
3. Get an Authenticator!!!! The mobile device version is FREE and the keychain is only $6.50 in the US with free shipping.
4. Consider SMS Protect - this is not an Authenticator, but is a messaging service that lets you know about account changes and prevents some of them, such as an unauthorized email change.Request a rollback:
Submit a ticket using this https://us.battle.net/support/en/help/solution/d3/266
D3 > I think I was hacked > I want to request a restoration