Hi max.
I may be dreaming, but didn't you say last year that you were going down to the 40Mb product to save money? It was shortly before you then said you were moving to your parents...which I think was Oct or before that... but you had also said quite a few other things so I cant recall now.
As J0hn says I suspect you had a lower sync at some point and because you do have a static IP your Plusnet profile has got stuck. From personal experience, the Plusnet profile is ok at tracking the slower IP profiles but more often than not isnt too brilliant when it comes to them being increased and I've frequently had to request they change it manually.
Anyhow as others have said well done for not watching your stats and glad that you are feeling better.