With difficulty! They say the DLM decides the Target NM.
However, sometimes Orange do fix your Target NM. You need to somehow get in touch with their Fault Management Team to release it. Tho' I've never seen it as high as yours; maybe 15 dB.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC