Sudden drop in download speed

[#1]

My download speed has been a constant 11,000kb/s for the last few months. Since Tuesday though this has dropped to a constant 4,700kb/s. I haven't changed any of my equipment or connections, and the speed reading is the same from my desktop, laptop plugged directly into the router or laptop via wireless. The router stats indicate that the line speed is 16,500kb/s, with line attentuation 29.5db and Noise 3.8db. From memory these are my regular readings.
I have tried rebooting the router and reconnecting, and also switched off the router overnight and reconnected, but still down at 4,700kb/s
Could someone at Plusnet have a look please to see if there's been a change at your end.
Thanks

[#2]

What is your Current Line Speed https://portal.plus.net/my.html?action=data_transfer_speed ; ?

[#3]

Thanks,
Just checked.
Info is: Estimated line speed is 12mb (This may vary between 7Mb and 17Mb). Current line speed 4.9mb. Why would this have dropped so suddenly, and who can get it back to where it was?

[#4]

Hi,
I can see you called in yesterday and we've attributed the drop in speeds to some disconnections and that we've been able to up the line profile for you.
Let me know if that becomes a problem again.
Adam