updateObject definition :
<element name="updateObject">
<complexType>
<sequence>
<element name="sid" type="xsd:int"/>
<element name="objectHandle" type="xsd:string"/>
<element name="attrVals" type="impl:ArrayOfString"/>
<element name="attributes" type="impl:ArrayOfString"/>
</sequence>
</complexType>
</element>
As you can see there is no value for the creatorHandle. You can always use "Impersonate" before making the call but even then, with updateObject, you cannot specify the description of the change status activity (Or if yes, I am not aware how).
You should do :
updateObject : to change the status of the task
createActivityLog :to log why and by who the task status was updated
WS call :
Result : (The call was done with PAM,PAM account but appears as me since i've specified a creatorHandle)
Notification activity that you need to create (allow it for every type of object that has workflow task. ISS,CR,CHG) :