Re what happened to your account, I am sure my earlier hypothesis is correct. The timing of your product downgrade in relation to the bulk basic service upgrade, followed by a manual adjustment to correct any anomalies.
The person doing the corrections not being aware of an intervening phone conversation between you and someone at P8 agreeing you would remain on the accidentally regained 76/20.
That's roughly what I thought, however Pulse8"s system had me down as being on 76XL even though I was on their 38 product at the time.
I think they may have been guilty of placing orders on TTB without keeping their admin up to date and this certainly explains their incorrect January invoice, which was quickly sorted.
I think you may be correct in that TTB were actioning the product regrades in a two stage process and were moving me from the old 38 product to the new 76 and then downgrading me to 38.
I'm back on the 76 product this morning and getting much better results again (although seeing some variability from test to test.
A good one:
and a not quite as good one:
Firefox on my work Win7 laptop is doing something altogether more bizaar with constant single thread and multi thread speeds, but with the multi thread significantly slower than the single thread speeds.