My account got hacked

Tonight around 6-7pm PST my account got hacked didn't know till my guild leader messaged me on discord asking why I left the guild. They used up all the crystals I had saved up which was around 3k changed the name of the account and spent all the energy I saved up on who knows what cause I couldn't figure that out. I went and changed my security setting for my Google stuff in case they got in that way. Was mentioned by my guild I should say something here about it anyway I hope I can get some help with this.