I still see advertisements even though I have already purchased Remove-Advertisements product.

If you see advertisements on new devices, even though you have purchased Ads Free service, you can restore purchase record.
Please refer to below.

[Android]
1. Sign in to Google Play Store with the Google ID you have subscribed Smart or Pro.
2. Delete Polaris Office and install the app again please. You can download it from Google Play Store.
3. Sign in to Polaris Office.
4. Select the Use Advanced Editing Functions  on top  > Select the 3dot on the top right > Select Use Past Payment Information on top right.

[iOS]
1. Sign in to App Store with the Apple ID you have subscribed Smart or Pro.
2. Delete Polaris Office and install the app again please. You can download it from App Store.
3. Sign in to Polaris Office
4. Select the Learn Pro features on top > Select Restore on the top right