Suddenly Struggling To Get 0.5 Mbps

[#1]

When I first signed up to plusnet I was getting speeds of approx 0.6 Mbps. After consultation & plugging my router directly to the test socket I was getting approx 1.7 Mbps.
About 2 months ago I gradually built up to speeds of approx 4 Mbps which I was delighted with.
The last couple of days however I'm not even getting 0.5 Mbps, but nothing has changed on my setup.
The figures below mean nothing to me so any help will be appreciated.

Below are my router stats :
Uptime: 0 days, 5:15:43
DSL Type: G.992.5 annex A
Bandwidth (Up/Down) [kbps/kbps]: 444 / 1,152
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 12.0 / 17.5
Line Attenuation (Up/Down) [dB]: 24.5 / 45.0
SN Margin (Up/Down) [dB]: 15.5 / 22.5
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 35 / 0
Loss of Signal (Local/Remote): 3 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 3 / 0
FEC Errors (Up/Down): 0 / 0
CRC Errors (Up/Down): 0 / 2
HEC Errors (Up/Down): 133,472 / 1

Below is the result of my BT Speedtest :

Test1 comprises of two tests
1. Best Effort Test:  -provides background information.
Download Speed
385 Kbps

0 Kbps 500 Kbps
Max Achievable Speed
Download speedachieved during the test was - 385 Kbps
For your connection, the acceptable range of speedsis 100-500 Kbps.
Additional Information:
Your DSL Connection Rate :1152 Kbps(DOWN-STREAM), 444 Kbps(UP-STREAM)
IP Profile for your line is - 500 Kbps
The throughput of Best Efforts (BE) classes achieved during the test is - 11.62:27.95:60.57 (SBE:NBE:PBE)
These figures represent the ratio while sententiously passing Sub BE, Normal BE and Priority BE marked traffic.
The results of this test will vary depending on the way your ISP has decided to use these traffic classes.
2. Upstream Test:  -provides background information.
Upload Speed
318 Kbps

0 Kbps 444 Kbps
Max Achievable Speed
>Upload speed achieved during the test was - 318 Kbps
Additional Information:
Upstream Rate IP profile on your line is - 444 Kbps

Below is my current speed :

Telephone number:
***********
Phone exchange:
BRIDGEND
Estimated line speed:
5 - Checked on 2010-05-26 23:28:01
Current line speed:
500

[#2]

Hi bluebirds1927,
Your connection has been shockingly intermittent of late. I would suggest visiting our troubleshooting guide for some tips on how to remedy that. If those suggestions fail then you have an option to raise a fault down the page.
Jojo

[#3]

The answer is that due to a perceived instability (too many resyncs) the exchange equipment has decided your line is unstable and has capped the speed at 1152kbps which is not as low as the IP profile which must have been caused by an even lower sync event.
I don't know if the HEC errors are being reported correctly but, if they are, you have a problem.
Are you still connected to the test socket.
Do you have another filter/router to try.
If you are connected to the test socket you will need to report a fault as something is badly wrong

[#4]

Thanks for the quick replies.
I have kept my router connected to the test socket since my original problems & have changed the filter without any success. Unfortunately I don't have another router to try. Do you think it's possible that the router could be the problem?

[#5]

I am sure Plusnet will offer a test router as it just may be the cause

[#6]

Well spotted Jim, I've just checked and it is banded.