New account with SuperSlow Fibre Broadband

[#1]

So I recently got another one of my clients signed up with plus.net. We all got very excited when we saw the estimated speed being offered between 66 & 68mbps. This shouldn't be a surprise as the site is only a couple of hundred meters away from the Green Cabinet.
3 days before the new phone line and broadband installation we got an email from plusnet support advising up of our speeds . . .
"Estimated line speed: 4Mbps  and Current line speed: 78Mbps"
When the Open Reach engineer installed the broadband, he tested the line and reported a supported speed of 78mbps. Now that seems pretty good for an up to 80 service.
This all sounds too good to be true . . . . and yes it is. I visited the site this week and ran a few BT wholesale speed tests which delivered speeds of between 14 and 15mbps.
So how does a pre-sales estimate of 66 drop to 4 once signed up and why does a line that supports 78 only deliver 14?

[#2]

The first part is easy
The speed estimate is for ADSL not fibre
The second part is more difficult - was that tested wired or wireless

[#3]

Thanks Oldjim, but you've confused me. When you buy a fibre product they give you an estimate based on a non-fibre product? Isn't that like buying a car with a 2.0ltr petrol engine and they quote you the performance figures on the 1.6 diesel?

The speed test was wired. The set up only has the OpenReach modem, a netgear router and a PC connected on gigabit LAN.

[#4]

I know but it is the Plusnet system - all screwed up but nobody seems to want to fix it
Regarding the speed - if you can post a ticket number from the account the staff on here will be able to have a look - unless you used that account to sign on to the forums then it will be linked and traceable