Handy with 2420 mAh is being charged by 40% times before the Power Bank is empty

Update:
After I wrote my review, this was asking me to [email protected] to turn, commented. This I did and received a replacement device after a short e-mail traffic that actually works better. It charges my phone almost complete and will be during the charging process is not nearly as hot as the first device. While it's still not quite the power that I have hoped from the Power Bank, but a state with whom I can live. So I change my original 1-Star rating from.

Original Review:
I do not know if I possibly impose a fallacy, the provider you get even on request no answer. In the product description is ".... Extra high capacity (3000 mAh) and a 85% efficient power output ...". Assuming I counted before buying. My phone (Lumia 930) has a battery capacity of 2420 mAh. The Power Bank 3000 mAh and if I interpret the description correctly, 85% of them also to the phone are delivered - that is 2550 mAh. So I'd have the phone at full power bank min. 1x can completely load.
I have the power bank fully charged several times. Basically, my phone is (at full power bank) charged only 40% before the Power Bank is empty. I have asked about Amazon accordingly a "customer question" and on weekends to get the info-mail that they can not be answered.
I am very disappointed with the product and will in future avoid products from this agent.