Swift: writeToFile does not save file on iOS device

I have a string I read from a text file: text = String(contentsOfFile: path!, encoding: NSUTF8StringEncoding, error: nil)!. Using println(text) I get the output "some text".

Now I also have another string otherSting = "other text". What I want to do is save this text to the text file. I tried using otherText.writeToFile(path!, atomically: true, encoding: NSUTF8StringEncoding, error: nil) and then reading the text file again. When trying on the iOS Simulator I get the output I expected: "other text". But when executing the same app on my iPhone i still get "some text". Does anybody know what I am doing wrong?

Edit:

I also tried using otherText.writeToURL(url!, atomically: true, encoding: NSUTF8StringEncoding, error: nil)with the same results.

Thanks in advance