Poor performance and speed since 21CN Update.

Question

My Wholesale exchange was upgraded to BT21CN at the end of January. (MELLOR, LANCASHIRE)
Before the upgrade :
> We got about 6-7Mbps constantly. (BT Unlimited Broadband).  This was day and night via Speedtest.net and BT Speedtest
> iPlayer and other services reliably streamed in HD at any time of day.
> We didnt have any speed drops at night and could stream video content etc perfectly for years.
Now everything has changed.......
After the Update 31/01/14 :
> Video from outside the UK is slow and constantly buffers. US Netflix for example no longer streams reliably.
> Video and streming services from within the UK arent that great either. iPlayer and other services struggle to stream in HD - if ever. 
> BT Speedtest says we get around 17-18Mbps. Speedtest.net Constantly says less than 5Mbps. BBC iPlayer speed tests only register 1.8Mbps. - we cant stream any HD Olympic services.
> After 4pm speeds drop across the range of activities, video services like youtube, iplayer, netflix etc etc dont work unless the streaming quality is very low.
> At night other Speedtest services report <3-4Mbps. BT still says above 17Mbps, buit we cant even use video and the internet feels slow.
>IP Profile is 19.34Mbps.
We pay for full unlimited BT Broadband however since the change to 21CN and a 20Mbps connection our service is now worse ! It almost feels as if we are being penalised or throttled for video and anything from outside the UK
BT Speedtest is the only one that ever says we get high speeds- but we dont, we cant even reliably stream video.
Cany anyone help??

Answer 1

MY CURRENT STATS (09/02/2014) ....
ADSL Line Status
Connection Information
Line state:
Connected
Connection time:
0 days, 04:12:22
Downstream:
16.47 Mbps
Upstream:
1.134 Mbps
ADSL Settings
VPI/VCI:
0/38
Type:
PPPoA
Modulation:
G.992.5 Annex A
Latency type:
Interleaved
Noise margin (Down/Up):
7.1 dB / 7.1 dB
Line attenuation (Down/Up):
9.7 dB / 5.5 dB
Output power (Down/Up):
19.9 dBm / 12.4 dBm
FEC Events (Down/Up):
3 / 0
CRC Events (Down/Up):
0 / 1
BTW PERFORMANCE TEST:
 Download speedachieved during the test was - 13.39 Mbps
 For your connection, the acceptable range of speeds is 4 Mbps-21 Mbps.
 IP Profile for your line is - 19.34 Mbps
Upload speed achieved during the test was - 0.91Mbps
 Additional Information:
 Upstream Rate IP profile on your line is - 0.83 Mbps
 SPEEDTEST.NET to Closest Server
Download Speed : 4.7Mbps
Upload Speed : 0.94Mbps
PING: 50ms
BBC iPlayer Speed Test:
Download Speed : 11.3Mbps
Streaming Speed 1 : 5.01Mbps
Streaming Speed 2 : 1.4Mbps
Streaming Speed 3 : 0.6Mbps
Your Connection : 2.3Mbps
TV-HD - NO
TV-SD - YES