I have enabled Cortana on my windows 10 pc but the voice pack is Windows Zira mobile. I can only choose from the 6 available but none of them sound like Cortana.
None of them sound like Cortana, because Cortana is not a voice pack. Cortana's responses, replies, and basic speech is an actual human recorded voice for the most part. When she has to say something that Microsoft hasn't predicted she would say, she will use Zira as the voice.