No, AncestryDNA is not useful for mtDNA. In my opinion, the only viable choice right now is the FTDNA Full Sequence mtDNA test. Recently, it was down to $139, and I imagine it will be back to that in the next round of sales, closer to Mother's day or thereabouts.
It's probably not the only choice, but it has to be similar in that it tests ALL of the mitochondrial DNA ring, all 16500 odd bases, *and* provides detailed results such as ALL of your mutations, insertions, deletions, etc. The LivingDNA and 23&Me tests only provide haplogroups, not the actual mutations/variants. Haplogroups are somewhat useful, to provide negative proof, show no possible match as you did, but they are not good enough for actual matching, except perhaps to tell you that you're on the right track, that it's worth testing further.