If this happens then you are trying to access the store with a different account. Ensure you sign in with the same account you used to buy the app the first time.
We cannot help you with this, as the “purchase relationship and history” is between you and the store.
You can also check whether you have purchased only the App or also the premium features. There is a different (smaller) price to pay for premium features, so if you never purchased them, this could be the extra price being asked.
If you purchased the app on a different store (e.g. you purchased on App Store with an iPhone and now you’re on Play Store by Google) then you will have to purchase the App again, because different stores don’t communicate between each other (it’s like if you’d purchased a movie from Amazon Prime and now you’re trying to watch the movie from Sky or Netflix. they are 2 different companies).