I recently had my STB go wrong.
Called NTL - 10 min wait - CS agreed STB was duff. I was offered next day call, but went for the day after. Eng turned up within timeslot, changed STB (already had RF bypass as requested to CS!). Said there were hit delays on the network and to call back if it hadn't picked up my channels in a couple of hours.
Rang CS later, who said the new STB/card hadn't been registered

and should be sorted within 24/48 hrs.
Channels available sometime the next day and CS even rang to confirm it had worked!
Overall 8/10 for that NTL experience.