I think the problems with their call centre is that they are geared up to talk the average user who has no real computer or engineering skills, as soon as you try to tell them whats wrong they just get totally confused. I had this problem over my 'evening slowdown problem', all I got is "I'll get someone to check the line"
Eventually they put me through to someone in the UK who understood perfectly why it was unlikely to be the line but they'd do a full optimisation on that first and put a monitor on the line as well, a week after the house skt update I rang the guy who said they'd looked at the monitor that morning, agreed that there was a problem and blamed the rack in the exchange. They connected me to a different one and the problem was solved.
They really need an 'experts' call centre