Is it better to try to work through PPS phone support, or provide written response with all supporting forms and docs from return?

Scenario: for tax year 2015 return I prepared, taxpayer receives CP2000 last October showing two omissions of income:

1) $2K of interest (taxpayer acknowledges I was not provided with this info at time of preparation)

2) taxable earnings on QTP distribution in excess of basis, also about $2K

We agree with correction number one. We don't agree with #2, and respond in writing by providing the QTP distribution worksheet that probably should have been provided with original return, all documents signed exactly as instructed in CP2000 letter. The QTP worksheet shows that entire distribution was less than qualified expenses, so none is taxable.

Now, 3 months later, a second CP2000 arrives saying "we received your response". But not only did they not correct the QTP taxable amount (they completely ignored the response), now the "shown on return" computation column no longer even matches the actual original return as filed. So without changing anything based on response, they still changed something, in error. Also, the new calculation is way off, there is now a PTC calculation that is totally bogus, both under "as shown on return" and "IRS corrected". Looking back at the first letter, there were probably some bad numbers in the "IRS corrected" column too, but we were just trying to correct the missing income problem, assuming everything else would pop up correctly after that. Taxpayer only owes a little over $200 additional tax, but 2nd letter now shows bogus amount over $1,500 due.

Note that this is not a matter of interpreting tax law or record-keeping, it is simply an error in processing the return. I have 3rd party authorization on the return, and have used that before with PPS to fix certain problems. I have also sent in letters signed by taxpayer to fix problems, and have had that work too.