For those of you who have looked at my two previous posts on this, here is an update.
Today I went to the local/nearby IRS office and met with two individual persons. The first guy admitted he had only been with the IRS for 8 months and that I needed to talk to someone with more experience. That person turned out to be a very pleasant lady who strightened things out in about 25 minutes.
It seems the IRS had NOT credited my two advance/estimated tax payments for 2010 to my 2010 accoutn, but put them into my 2009 account. This despite the fact that the checks and accompanying paperwork were prominently marked for 2010. Then, they discovered their mistake and fixed things up by crediting the $ to 2010. But, their internal software can't do thing like that without generating letters to the customer, and that is why we got the theree preceeding letters. The IRS lady printed out copies of both my 2009 and 2010 accounts and gave them to me as "proof" that things were now ok and I could ignore the notice to pay the $10,125.
So, now I'll wait and see if my refund check does come by the end of April as she assured me it would. It's good I'm semi-retired so I have the time to do all this extra running around to get things straightened out!!!