If you’re only 2 miles from exchange, ring Sky. They will try to ramp the speeds up manually. The Sky routers are designed to find the fastest speed that is reliable and keep it there. If there is a fault on the line during the test it will stop where ever it has got to. Mine did similar and I was stuck at about 2.5Mb/s, after call running at 17.8Mb/s at about 2.5 miles from exchange. Very happy with them, my parents are on same service but closer to exchange. They get 18.9Mb/s.
As for the reputation for Sky’s customer services being crap, I have always found them very quick and friendly. Unlike Virgin, who it once took me 45 mins to convince I was a customer!