The line attenuation down has instantly increased from 6.5dB to 22dB. ... (The line attenuation down has actually decreased marginally to 4.8dB.)
There's something fishy there. Normally Down attn. increases by about 3dB when upgrading to ADSL2+. Also normally Down attn. is about 2 x Up.
This would suggest that your down attn. should read about 10dB, which would fit the +3dB increase.
My SNR is 28.0dB (up) and 22.1dB (down)
Indicates your ISP is capping you with an unnecessarily high NM to a low speed.
Your ISP has you on a peculiar profile!
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 20 Meg WBC