I'm currently trying to learn C# so I can eventually develop a 2D Platformer, I was learning how to use Java but once I noticed that it was probably going to be a huge waste of time I moved onto XNA.
Java and C# are so similar that you could learn Java exclusively, then jump to C#/XNA with only a few minor hiccups. That's how I did it, anyway. Most of what you're learning when you're learning your first programming language isn't the language itself, it's programming logic--it's transferable to any other language. The rest is syntax and libraries and such, which will differ, but in this case (Java to C#) not by very much. Depending upon how far you got with Java, you'll either want to read one of these free eBooks (not far at all) or this not-free reference (pretty far).
As others have said, yes, Microsoft dropped XNA (a bizarrely bad decision, IMO, but they seem to be making a lot of those lately). That doesn't mean it's not still a good way to learn game programming. Like others have said, MonoGame doesn't seem to be going away either. Even if it does, that's still not going to render any knowledge acquired while using XNA useless.
Note: I do notice I put the bar quite high when I talk about creating a 2D platformer even though I haven't even started using XNA yet, I only included it incase anyone was curious for some unknown reason.
That's actually exactly what I'm working on right now, although I made a few other games via an XNA tutorial book before starting (and before that, a text adventure and minesweeper clone in Java). There's nothing wrong with setting the bar a little too high, as long as it's within reason--you're more likely to keep working at something that's interesting but a little too advanced than you are something that's fairly easy but boring, in my experience. Start right out with "how do i maek skyrim," though... that doesn't end well.