Here is my story.
Please don't stop reading half way, this could help you.
I have been with Telecom adsl2+ plan(s) since they introduced it.
Despite my Line Attenuation being 26.5dB, I was only getting ~6.5Mbps.
I do realise reaching theoretical speed is not possible and there is more to it than just Line Attenuation. i.e.) SNR, phone line quality, etc
Not long after joining the plan, I noticed my broadband speed was well below what it should be when I compared it with Theoretical Speed vs. Line Attenuation ADSL2+ chart, ~15Mbps for ~25dB.
Out of curiosity, I called Telecom at the time.
The response I got was that the line is working fine and that there are other factors that influence broadband speed, so I settled with the speed I was getting.
A few years passed which in that time I made numerous calls to Telecom due to minor broadband issues, but the broadband speed was steady.
This was till 3 months ago.
My broadband started syncing at 3Mbps, and when it did sync at 6.5Mbps the connection only lasted ~30minutes.
Response I got from Telecom when I called 1 month ago was "Turn off your modem for 5minutes, and turn it back on."
A single hard reboot did the trick, but the problem persisted after I hung up the phone.
I even tried different adsl2+ modem, but no improvement.
The lowest recorded speed was 1.7Mbps, which was this morning. (April 11th 2014)
I called Telecom again today, and a Chorus technician dropped by soon after to investigate.
Initially, his work seemed no different to all the technicians I had in the past.
All he told me was that all the lines are working fine, and it must be the house alarm that is causing interefence.
This was until he checked the street power pole just outside my house.
He told me that my phone line was stretched too tight to the power pole joint and the joint itself was also poorly positioned and damaged.
I checked my broadband speed after he finished repairing the joint and phone line.
I was shocked to see the broadband sync at 12Mbps.
It has been 2 hours since the technician left, and the connection is still solid.
I will need to give it more time to see whether the connection is stable or not.
My point is, don't settle for what Telecom tells you over the phone.
Those people only know as much as what ADSL2+ stats should look like, but thats about it.
Ask them to send a technician over if you are not satisfied and get them to investigate thoroughly.
I do not have a copy of my previous ADSL2+ statistics, but here is my current.
Line Coding(Trellis): On On
SNR Margin (0.1 dB): 118 79
Attenuation (0.1 dB): 265 130
Output Power (0.1 dBm): 191 121
Attainable Rate (Kbps): 14052 748
Current Rate (Kbps): 12096 1049
As you can see Attainable is 14Mbps, but actual downstream rate is 12Mbps.