If the line is only 50m then the upstream is very low. Either there is something not quite right with the line or it is going "around the houses" (literally) from the cab to your property.
What do the estimates on the BT Wholesale Checker
say for your phone number? If you copy and paste the results remember to remove the phone number from the paste.
EDIT : Oops, typo - downstream in first paragraph should have said upstream. Fixed
Edited by ian72 (Fri 21-Jul-17 12:58:13)