I can’t see any way to contact the app provider.
The app keeps forgetting I’ve paid to stop all adverts. When I paid and when I reinstalled the app and restored purchases all adverts disappeared including the one for double coins but leaving the app and reopening it after using other apps only the banner at the bottom and the pop up adverts were disabled - if I want double coins I have to watch an advert ( using restore purchases will not fix this unless I uninstall and reinstall the app ) .