From my experience Talk Talk and Dido Harding are a pair of absolute ****s.
My Father was in hospital, dying, and somehow my mums phone gets disconnected. Real pain as she may get a call at any moment saying that my dad is about to go. She phones up to report this on her mobile, and they deny there is any problem. Eventually, she persuades them that there is a problem. Turns out that one of her neighbours was changing from TT to Sky and they had disconnected her number by mistake. So she says "why not just turn it back on?". The response was staggering. Apparently it would take one month and she wouldn't have her old number!
Now my Dad was very involved in local politics for many years and loads of people were phoning my mum to find out how he was. She couldn't even email people as her internet was gone as well. TT weren't interested at all in helping her. She had even just paid the line rental in advance!
Anyway Sky get in touch as a neighbour had told them what had happened. They apologise for the changeover going wrong, even though it wasn't their fault, and offer to take her on at a massive reduction and do it in a week on her old number. So she goes to them and has been for nearly 2 years now.
TT refused to pay back any money, even after we contacted Dido, for not providing the service that it was paid to do, until 6 months later and many, many calls and letters.
As I said a pair of absolute ****s.