Hi Sharon, what was your mtDNA? 23andme doesn't tend to calculate it out very far. I tested at 23andme and got U6a7 for mine, which doesn't tell me too much, just that my maternal line comes from Northern Africa and that there may be a Sephardic component (I'm Ashkenazi as far as I know).
I don't know what you mean about an Ashkenazi mtDNA because I don't believe there are any, to the level that 23andme reports. Of course, 23andme, does the full autosomal too; is it possible you're reading a report about that and thinking it's from mtDNA?
One cool thing is that, even though 23andme doesn't give you a long mtDNA report, you can still figure out the sub-sub claves and categories from the raw data. I did it and discovered that my full mtDNA doesn't stop at U6a7. It's U6a7a1b, which is a known Sephardic cluster from about 500 years ago.
I am not sure if I can do an outside link but I blogged how I did this and you can do it yourself as well. Figuring out how to do it was not easy but, now that I know, it's just a matter of tracking down the data. It's at norwitz.net.