I bought a product through the Air Navigation Services website and I can’t find it in the Map Store.

Purchases and subscriptions done through https://services.airnavigation.aero are stored in your Air Navigation Services account. 

In order to access them in your app, you need to login to your account from the app. In order to do so, go to Configuration > Account. 

After successfully logging in:

iOS: Configuration > Store > Restore > Click on the charts/package of your choice and it will download. 
Android: Configuration > Installed data > Restore > Click on the charts/package to download them.