Having only just seen this.
The customers actual issue was that they had opted for an Annex M service on a line that was just not suitable for it. We had made suggestions for us to change it (as far back as May 2014, which was also the first contact of a speed issue), free of charge, to a non-Annex M service which would restore the balance and increase downstream speeds but despite offering this on a number of instances, it was not taken up.
Whilst the customer did raise this with us on three instances via our portal, they never responded to us when we asked for more information from them. We sent reminders before the ticket automatically closed, prompting to provide us with the information we needed to help but no reply was forthcoming.
Essentially, the speed issue seen was down to the product chosen rather than a poorly performing service.