There is a big difference between “hearing voices” and hearing God. People can hear any old kind of crazy voice in their heads.
But when God speaks, it is an inner voice within the human spirit, not the head. It is steady, calm, and with authority. God’s voice doesn’t plead, or beg, or whine, or condemn. God simply speaks.
His voice is self-authenticating and carries with it the inclination to obey. The “content” of God’s voice is always consistent with Scripture.
Granted, there have been and are disturbed people who obey the “voices” in the head, sometimes claiming it was God or the Devil or whoever.
But the counterfeit does not nullify the genuine!