We need to try the following steps to *force* the correct answer from Google Billing.
1) Clear Textra from the recents / task list.
2) Android Settings > Apps > 'Google Play Store', [Force Stop] and then Storage > [Clear Storage/Data] then open the Google Play app and press Accept.
If not, check if you have multiple Google Play accounts, then see which one you purchased under (as you must be logged into that account in Google Play or purchase on multiple accounts, that's just a google thing not us!). If you have multiple accounts, consider removing ones you no longer need. Ensure you are logged into Google Play with the account you purchased under.
Still not working? Try an uninstall of Textra, restart your phone and see if that works.