Speed variations on ADSL2+

[#1]

I'm on ADSL2+ and usually get a solid 16Mbps download speed.  However over the last week or so the speed has varied from normal to atrocious and I'm not sure why   The only recent change is a newer Netgear router - the old DGND3300 died and I had to get a Netgear D6400.
Link speed is good:
ADSL Link         Downstream    Upstream
Connection Speed 20745 kbps 1235 kbps
Line Attenuation 13.0 db         5.7 db
Noise Margin         3.1 db         5.8 db
The router usually maintains a rock solid connection.  I cant even get on the btwholesale speed test page.
Anything that can be checked at the Plusnet end?

[#2]

Is that wired or wireless?
If wireless you may have dropped on to a sometimes congested channel with the change of router.

[#3]

The BT.com and BTWholesale.com websites seem to be down at the minute, so that's probably why you can't access the btwholesale speed tester.

[#4]

Quote from: JayG

Is that wired or wireless? If wireless you may have dropped on to a sometimes congested channel with the change of router.

Thanks, I just had the same thought so have changed wireless channels and will see how that goes.