I have to say that even beats my line length of 9km. But what router did you have? The Business hub or the billion 7800N have been reccomended to me by an engineer for getting some sort of a connection of broadband even when the engineer's equiptment wouldn't.
This. I'm on 9km+ and have used the following routers over the years. In the order tried, approximate sync speeds were...
HH1 - about 1200 kbps
2Wire 2700 - about 1600 kbps
HH2A - About 16-1800 kbps
HH2B - About 13-1400 kbps
Voyager 2500v - 1800-2100
I've not tried the Billion, but can thoroughly recommend trying the Business Hub (2Wre 2700 HGV, go to ebay and spend £5). The voyager is harder to get and probably not necessary in your case.
Once you have one, re-place an order and try to get sync with that.
And the standard approach to get the best from the wiring...
Disconnect any diallers (oil tank, alarm, etc) from the line.*
Disconnect all extension wiring.*
If you don't have an NTE5 master socket, get one fitted.
Use an Openreach faceplate filter.
At these sorrt of distances, getting everything sorted out could make all the difference.
*You can reconnect later, to try and get adsl working it's best to just remove them.