Yes, I think your explanation fits my experience well. The trouble is, as Plusnet has increased its customer base and, in line with that, its customer service team, it is becoming increasingly difficult to get through to a more experienced member of staff. So far, with my current problem, I haven't managed it. Even the plusnet forum, which used to be a good alternative to phoning in, is no longer coping.
I notice that they are currently advertising for Customer Support Advisers at a salary of £16,000 with a possible bonus of 'up to' £400 a month. I can't help wondering whether the way that bonus is structured is part of the problem (numbers dealt with or solving the problem?), and whether it could be used to help solve it. Plusnet occasionally send me a link to a surveymonkey 'satisfaction' survey after I have dealt with their staff - the last two times I got this, I couldn't complete it because it told me I already had...
In a slightly different setting, I have always been very happy with Amazon's customer service team, even though they are off-shore - but then they ALWAYS ask for feedback.

I notice that your stats, on plusnet, showed ADSL2 G992.3.
Have read of subscribers having similar problems when router changed from G992.5 to G992.3
Maybe more experienced could advise whether requesting return to ADSL2+ would be of benefit.
This assumes you are on CN21 and router stats still showing ADSL2
Also read of AAISP resolving a similar Plusnet problem. Related to ADSL Max Premium and Marconi DSLAM.

If your statement on wages are true. Then IMO peanuts and monkeys applies. The software company I worked for paid 3 x that for support engineers.

They are first line telephone support not "support engineers". When you have a large customer base then paying significant wages for what is effectively a telephone answering service is a no-go. Generally first line call centre are low paid and not overly technical - second line are more technical and might earn double that but not until you hit 3rd line and above would you start paying those sorts of wages in most larger IT organisations.

ADSL2 mode (G.992.3) is only available on 21CN

If property prices in Sheffield are cheap then almost tempted to move.

In reply to a post by MrSaffron:

If property prices in Sheffield are cheap then almost tempted to move.

If you go to Dore and Totley which border the Peak District, you will find some very nice and very expensive properties. Mind you compared to London I suppose they are cheap....