When is your experience of plusnet from? They have had their problems in the past but in general they are pretty good these days. Customer support can still be a little problem but the support you get from the plusnet reps on this site is usually first rate.
You imply that PN have improved - can you tell me what timescale you are referring to?
My own experience, approx 1 year ago, was diabolical!
I went through a saga of PN failing to provide (but arguing that they had), eventually getting them to agree there was a problem & agree to correct it - but then fail to correct it. Eventually connecting me onto the wrong (much slower service) but arguing that it was caused by the extreme length of my line (my line is ONLY 500m to the exchange), etc etc etc.
All in all, over the course of just ONE MONTH, no less than 69 tickets were raised with PN trying to close most of them before they were resolved!
In the end I gave up & demanded my MAC - even then they failed to supply that when requested!!
In summary, I really do hope that PN's service has changed, but please excuse my scepticism!