Howdy. It might be easier to rebuild the entire Pivot Table with each update. If you look at Chapter 12 of VBA and Macros for MS Excel, by Bill Jelen, et al you will find all that you need. It not only explains the updating process, but provides several working examples. It actually is as fast as trying to update one item, and it cleans out all the other stuff that accumulates when trying to update. Once I began using that approach, it solved several other problems as well, such as getting around the limitations of the Pivot Tables.
For me, it was worth buying the book for that chapter alone.
old, slow, and confused
but at least I'm inconsistent!