What download speed you're getting on the XBOX? Please post a screen shot on this thread also a test on desktop/laptop or using smart phone using (www.speedtest.net) for testing purposes.
Feel free to send me your details so we can proceed with further investigation.
I have the same problem, but found that if you connect your xbox through a VPN it should download as expected, but you shouldn't have to use a VPN for your service to work as it should. Also downloading through windows store has the same problem that a VPN can fix