Speed dropped by 20Mbps.. support not interested

Question

BT Wholesale checker estimates that I should receive 53.3Mbps.
When I first had Infinity installed I was consistently achieving above 67Mbps with no problems. Great!
Unfortunately, as my line developed a line fault the day before the day of the install, I chose to let the engineer arrive, on the hope he could fix the line fault and install Infinity. The engineer said he was "not a voice engineer" so just connected everything up, acknowledged that there was an issue and left. As soon as he left, I quickly unplugged the modem and left it off until I knew the line fault had been fixed.
The line fault was fixed in 48hrs and I was able to enjoy 67Mbps for a few weeks when the line fault returned. As a result the line speed slowed. Originally, dropping me from 67Mbps to 55Mbps. The engineer said the line profile would reset automatically after the fault was fixed.. however it has never recovered. The speed has since dropped again to 41Mbps.
This is taking the biscuit really, considering I know I can achieve at least the promised 53.3Mbps!! some 20Mbps more than I currently can achieve.
The uptimes between syncs are always well above the 5 week mark, so I don't believe it's due to frequent disconnects. As far as I'm aware there are no issues with the line, (I certainly can't hear any crackle or hiss on the phone), but people ringing the house do complain that I am very "quiet", so I tend not to use it. This, and the SNR tends to drop 2-3dB when the phone is off the hook.
I've called support whose stance is essentially.. "You are within the limits of your estimated speed" and that is it. No further help. They aren't interested that I know the line is capable of above 55Mbps, only that 41Mbps is "acceptable". I'd take 53Mbps all day long, as anything more was a bonus.. but I'm not happy with knowing I've dropped over 20Mbps due to a line fault outside of my control, and they aren't even willing to help reset the line.
/rant
e: It's probably best to mention that I only have 1 master socket, so the line comes direct underground to the socket under the stairs, and in to the openreach modem. I use an Asus RT-N66U as a wireless router, but the house is wired with Cat6. All speedtests are completed on a PC on the wired gigabit network to rule out wireless issues.

Answer 1

Welcome to BT (maybe) Infinity (sometimes), as with most of these posts, and I am sorry if I offer now help to your problem what so ever, it will be swept under the carpet and forgotten, if BT said what they have said that is all you will get, end off.
Personally I was promised a gaming quality connection, its been s..hit since December 2012, and if your ping is not over 100 ms they will do nothing, if your speed is not below 16Mbps they will do nothing.
It's all in the small print.
Also I/you will be hit by the guru's for speaking the truth (out of line) about the situation.
Rant over , swept away by BT, and forgotten.
What's slow about FTTC........DLM