After updating the app billing lib to implementation 'com.android.billingclient:billing:2.0.1' I started to see refunds even after 3 days. How is that possible? Google only mentions here that purchse is refunded if user uninstall the app in short period after purchase. I guess 3 days is not a short period.
Users must acknowledge the purchase within 3 days otherwise the subscription will be refunded:
https://developer.android.com/google/play/billing/billing_library_overview#acknowledge