Not sure how you got this response. I used the same as you did and I got
"Uneven name-value pairs to update"
what you should use is"
<attrVals>
<!--1 or more repetitions:-->
<string>name</string>
<string>testing</string>
</attrVals>
"
But that should not be the reason why you original script failed on this method. Can you show us the contact detail of
ServiceDesk contact?