Welcome to Android Central! This is one of the most common questions on this forum, but it seems the posters never give enough details for us to help definitively.
In addition to telling us which device you have, tell us specifically which emoji app you installed, and from where. Is this an "Emoji Phone" app? In the past, that's been notorious for being difficult to uninstall, probably because the developer wants to keep throwing ads at you (and hopefully nothing more malicious).