Without knowing what your line can support your post is meaningless.
Just because you are on a 50Mbps package does not mean that your line can support that. You will only ever get the speed that your line can support regardless of what package you are on.
If you carry out the following it will give people a chance of helping you.
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 post the stats from 1-12 by logging onto the Homehub management pages then troubleshooting > helpdesk. http://bthomehub.home/
If you have the Smart Hub, can you go to hub manager then advanced then technical log and post the stats. http://bthomehub.home/
Is there any noise on your phone line? Dial 17070 and select option 2, there should be no noise between the announcements.
Try connecting to the master socket/ test socket and if your problem is still there it could indicate that there is a line fault before the test socket on BT's side.
When you use the test socket make sure that any telephone extensions you have are "dead". There should be no dial tone at any of your phone extensions. If they have a dial tone it means you have star wiring and that is not good for VDSL Broadband and will need to be fixed.
The previous 18 months I was getting 45-60Mb. Had openreach engineers out 6 times. And every time they can’t find a problem. Replaced master socket/ line to DP pole.
Is the 6mb your connection speed shown on router or is it the download speed when downloading a file?