Why am I being asked to pay for the Oxford Dictionary of English when I have already subscribed?


Usually, once you change your device or update the software, yor Premium license does not restore automatically. After this, you may see a notification that asks you to subscribe. Even if you have purchased the Premium lifetime license some time ago, it still counts as lifetime with no need to subscribe. You would just have to restore your purchase. 

The article on How to restore your Premium license is available here