Installation of the full version of the app does not remove the free one from your device and it might be that you are still using the free one except the paid one.
The difference could be seen on the icon. The icon for the paid version of the app has a white border with a blue message bubble on it. The icon of the free version has a blue border with a white message bubble.
If you have any questions - please let us know at firstname.lastname@example.org.