Maybe, "Ah, that's sorted now". If we say "That's quite another matter," we mean that "that" is not relevant to the present situation, or that "that" is much more complex or difficult than what we can manage at the present time. It would sound very strange in the context you've just described.

Some good suggestions here! Most of the time I just say, "Oh that's (much) better!" but there are a few idioms that you could use like, "That makes a world of difference" or simply "What an improvement!"

Oh i get what you mean, we have something similar in italian, literally translates as "Ah, it's another thing!", to express qualitative difference. I think in english you have to be much more explicit, and have to say "Oh, there's no comparison to before", "Oh, much better", "Now it's perfect" or something similar. I can't think of a similar expression in english, some are close like "It's a whole 'nother level" but not really proper for your example (maybe if you compared a skype call to screaming to someone far away".

In Portuguese we use to say: "Agora está melhor". That's mean the same thing in English: "That's better now".