Slow speed/high SNR margin after upgrade to ADSL2+...

Question

I have an issue with slow speed that I am suspecting is caused by a high SNR margin (about 12dB) which has come about (I believe) due to the fact that my router was repeatedly reset during the first few days of the upgraded service. The exchange was upgraded to ADSL2+ on 3rd January.
I have a US Robotics 9108 which has worked fine for nearly six years. I was getting around 8Mbps before the upgrade which isn't far off the theoretical maximum.
There was a problem with my router and I only found it to be my router at fault over the last few days. Upgrading its firmware has cured the problem which was that requests weren't being fulfilled once connection had been established, (seemingly particularly when this was ADSL2+ or ADSL2 mode). Consequently, I reset my router in these instances and I believe that this will have been interpretted by the exchange as being due to line noise. In general, I disabled ADSL2 and 2+ modes on my router to force it back to G.DMT and it usually worked fine (albeit slow sync rate relative to that I had before 3rd January).
During fault conditions, the connection synced OK. I recently borrowed a router and tried it and it immediately connected faster than mine had done previously and I could access the web without issue. This confirmed that my US Robotics was at fault, and after downloading its latest firmware, it fixed the problem.
There is no bell wire as there are no hard wired extensions from the master socket. I use a single filter which plugs directly into the master socket (i.e. no extension lead to the filter).
I was using a BT filter (MF50) I got in 2004 when I first got broadband. This came with a Voyager 100 modem and is a rebranded YCL one. I have since replaced this with a Z350-UK which I have borrowed. The US Robotics didn't come with any filters.
With the BT filter, caller display does not work at all when the router is connected in ADSL2 mode. In G.DMT mode the problem with caller display was intermittent. The Z350-UK has rectified the problem with caller display not working when in ADSL2 mode. I have ordered a Pressac Interstitial VDSL Faceplate as a perminant solution.
Do I need to contact the support helpline to get this fixed? Or will the SNR margin drop over time? As I say, I got around 8Mbps before the upgrade.
I am presently connected in 2+ mode and stats are:
SNR margin (dB):
12.8 
5.4 
Attenuation (dB):
34.0 
12.0 
Output power (dBm):
0.0 
12.8 
Attainable rate (Kbps):
8984 
1144 
Rate (Kbps):
6495 
1144 
I have just run the BT Speed Test and the results are:
Test1 comprises of two tests
1. Best Effort Test: -provides background information.
Download  Speed
5282 Kbps
0 Kbps
7150 Kbps
Max Achievable Speed
 Download speedachieved during the test was - 5282 Kbps
 For your connection, the acceptable range of speeds is 2000-7150 Kbps.
 Additional Information:
 Your DSL Connection Rate :6495 Kbps(DOWN-STREAM), 1144 Kbps(UP-STREAM)
 IP Profile for your line is - 5730 Kbps
2. Upstream Test: -provides background information.
Upload Speed
938 Kbps
0 Kbps
1144 Kbps
Max Achievable Speed
>Upload speed achieved during the test was - 938 Kbps
 Additional Information:
 Upstream Rate IP profile on your line is - 1144 Kbps
We were unable to identify any performance problem with your service at this time.
It is possible that any problem you are currently, or had previously experienced may have been caused by traffic congestion on the Internet or by the server you were accessing responding slowly.
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Answer 1

once you have maintained 3 days + stable connection then you can contact the forum mods on this link and request a noise margin reset http://bt.custhelp.com/app/contact_email/c/4951
they normally reply by email or phone directly to you within 72 hours
you do not need to contact the helpline
They are a UK based BT specialist team who have a good record at getting problems solved
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