Huge drop in speed after signing new contract

[#1]

Have been experiencing really poor connection since renewing our broadband so have ran both the normal and advance tests.
Using BT's test user login for our router their results showed we could reach our potential speed from our local cabinet (around 14mbps)
whereas when connected to plusnet through the BT wholesale test site the maximum we could achieve was in the red zone of 2.53mbps.
How do i get this resolved as our internet has become unusable.
I have tried calling your customer support but still not through after 45mins on hold.

[#2]

well after an 1 hour 25 minutes of waiting on hold to customer Service the battery in my phone died 
Seriously can not believe i have been on hold that long and no one answered.

[#3]

Have you raised a fault online?  The "troubleshooter" requires you to answer all sorts of questions, seemingly irrelevant ones in some cases, but it's the only way to get it logged unless by good luck someone from Plusnet responds on this forum.

[#4]

Thank you aesmith, i have used their troubleshooter and the fault is logged.
I wished I'd reported this when the problems first started but i tried to be patient.

[#5]

Can you get statistics from your router, line speed and noise margins for example?  If you let us know what type of modem, we can help you get that info.  Also your "current speed" from the Plusnet member page here .. https://portal.plus.net/my.html?action=data_transfer_speed ; That's not actually your line speed, it's your "profile" which is the rate that Plusnet and BT think your line should be able to download, and the rate that your connection is therefore shaped at their end.
If you're running slow then it could either be that your actual connection is slow (as shown by the router statistics), or Plusnet have your account set to too low a speed, or something's got screwed up in the relationship between Plusnet's settings for you, and BT's activation of those settings (my line's in that state for example at the moment).