Thank you for reaching out to the Samsung community! We would like to inform you that It is the Google feature to unlock the device by voice assistant. You can disable the voice unlock feature from settings>>Lock screen and security>>Secure lock settings>>Smart lock>>Trusted voice>>Disable trusted voice.
Be sure to hit ♡ when you find an answer that works for you. For Further assistance, you can get in touch with us via Live Chat option by following- http://livechat.support.samsung.com/Customer_new/IN. You can also connect us via Samsung Members web community by following mentioned url-https://community.samsungmembers.com/en_IN#/
