First and foremost, it seems as if the app is not supported on OS 7 or on ur device.
If an unsupported app is installed it may cause instability / os crash as happened in ur case.
Now coming to your point, any vendor will first try to get ur fone repaired.
If that fails to rectify, then and only then they'll issue you a replacement device.
But, generally if you are firm enough with them, you'll get a replacement device.
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