Wild apples, natural yeast - help!

Hey all,
I decided to experiment with all natural cider and filled a carboy with cider pressed from some random trees. I put it in my shed Sept. 10, SG of 1.058 and titratable acid of .4%. It did some fizzing and built up a plug of foam initially and there was definitely some yeasty sediment at the bottom, but it soon seemed to stop fermenting. No bubbles were coming out of the airlock. I thought maybe it was too cold in the shed, so put it in my pantry last week. Not much change. So I checked the SG a couple of days ago, and it was still 1.058 and tasted almost the same as it did when pressed! (I did correct for temperature both times).

My first thought was that I should add a package of yeast, that my natural yeasts were not strong enough. So I bought some, but when I came home today it had foamed up again, filling the airlock!

I'm really not sure what I should do now or what the explanation is. Should I give these yeasts another chance? Should I add my champagne yeast? Are there dangers to it having sat around for so long not fermenting? It tasted fine, but obviously I never sulfited it.

Any advice welcome!

I'd go ahead and add yeast. Like I pointed out in another thread, apples typically don't have enough, or the right kind of yeast on them to really do a proper fermentation. People doing natural ferments are usually picking up the yeast from the wooden presses they have been using for ages.