I agree there are two totally different things, but I'd spell both of them "any more". Obviously there's the straightforward any + more where the two words have their separate meanings - I can't find any more mushrooms.

But the "any more" that's the negative of "still" is odd. I'd write it as two words "I don't do it any more", but can understand why you'd close it up: it doesn't much look like a compound. Well, sort of it is: "I did it some more" vs "I didn't do it any more". But apart from that it doesn't really behave as a compound of any and more, does it?