If you have subscribed to the Printify Premium plan, and yet you don't see the discounted prices, try logging out of your Printify account and then log back in. Then you should be able to see the new prices.
It may seem like nothing has changed, however, all the prices that are visible from that point forward are with the Premium plan discount applied. You'll know that's the case as you won't see the green text that mentions the Premium prices anymore.
If you have created an order prior to subscribing to Premium, and still see the old prices there - don't worry, the prices will change to the Premium prices once the order is sent to production. You will be charged the Premium price in that case as well.