Then if the user logs out from my website and another one logs in he's identified as the firstUser. (which means he sends message through conversations as the first user)
I tried using _hsq.push(['revokeCookieConsent']); to delete the cookies but it deletes all of them except for messagesUtk which seems to be the one causing the issue.
The revokeCookieConsent method now removes the messagesUtk cookie, allowing you to clear live chat identities on the same device. This change has been live since February 21, 2019.
To confirm, are you trying to follow the steps @cbarley mentions in this post, but finding that the messagesUtk cookie remains even after triggering_hsq.push(['revokeCookieConsent']);?
The revokeCookieConsent method now removes the messagesUtk cookie, allowing you to clear live chat identities on the same device. This change has been live since February 21, 2019.