You will only ever get the maximum that your line can support which in your case may only be 44Mbps.
Can you run this checker and post back a screen shot of the results. Make sure you delete your phone number before posting.
If you have a Homehub 5 can you also post the stats from 1-12 by logging onto the Homehub management pages then troubleshooting > helpdesk. http://bthomehub.home/