I've seen this many times in mangas, here's one example:
Context: A girl catches a thief that stole today's takings at the shop she's working at.
Thank you! 手伝ってくれてありがとう。
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It's a shortening of って言うの! or って言っているの! and shows some irritation on the part of the speaker. "What I'm telling you is . . .!" There's some good explanations here: http://oshiete.goo.ne.jp/qa/1847367.html