Your line length is more like 3.9 km on which you could get about 4 Meg.
Those disconnections on phone calls may be making the line seem unstable and keeping the NM high. You need to sort them out first.
Try swapping filters. Do you have filters on every phone? Have you removed the ring wire?
Do a BT Quiet Line Test by calling 17070 Option 2. If you hear any noise at all, report it to phone provider as a voice
, not BB, fault.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU BB => 2010: Orange 16 Meg LLU BB