That's another matter
Hello native English speakers)
I'd like to ask you about "Это другое дело" (That's another matter).
I had some conversation with american yesterday. I used the "that's another matter" and she didn't understand what I said.
The context was following. We couldn't set up the skype and at last we did it, I exclaimed "That's another matter"
Please, explain to me the real phrase that uses native speakers.