Having Trouble retrieving "otherMobile" LDAP attribute vb.net

Question

I am trying to retrieve "OtherMobile" attribute from AD. This is for an employee account recovery tool I am building. For some reason, I can't search on "otherMobile". Any ideas how? Thanks! my code:

Dim AD_entry As New DirectoryEntry("LDAP://", "username", "password", 
    AuthenticationTypes.Secure)
    Dim objSearcher As New System.DirectoryServices.DirectorySearcher(AD_entry)
    Dim search As New System.DirectoryServices.DirectorySearcher(AD_entry)
    search.Filter = "(&(objectClass=user)(otherMobile=" + txtSearch.Text.Trim() + "))"
    search.SearchScope = SearchScope.Subtree
    search.PropertiesToLoad.Add("otherMobile")
  
    Try
        Dim result As SearchResult = search.FindOne()