Skipped an achievement (kindle fire)

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One of the amazon game circle achievements was skipped over in my game. The achievement is "kill 100 enemies with machine guns" and it remains at 0% no matter how many kills I get. I have already gotten more than enough to receive the achievement as I got the other two for 50 kills and 250 kills with machine guns and use the machine gun exclusively.

Thank you I would be happy to give you any information that would help fix this.