This type of problem is the result of a caching issue.
When the plugin is deactivated or deleted, it will no longer run on your site, effective immediately. However, some sites have a caching system whereby old versions of the site continue to be shown to site visitors. This means that even though you have deactivated/deleted a plugin from your site, the cached (older) version of your site might still be shown to your visitors – and that older version of the site can be from a time when you still had the plugin active on your site.
Often times cached pages are served automatically via your web host, and many users are not aware of the fact that their web host does this.
If you are using wpengine (or a different host that auto-caches) try reaching out and ask if they can clear your cache for you.
Some times it takes a few hours after users take the above steps to notice the change. In this case, you should also clear your browser cache (though clearing your browser cache would only be effective after taking the above steps).
If you would like extra help with clearing the cache on your site, please feel free to message me direct justin[at]clevelandwebdeveloper[dot]com and I can try and provide further assistance.