Personally I can't see that many people having problems cancelling phone/broadband - moving it maybe but isn't that all done by the "gaining provider" these days?
The only people likely to have cancellation issues are those with Sky TV where (& they're on very dodgy grounds legally) Sky changed the T&Cs such that you have to cancel via phone for "security reasons". If you contested this in small claims court you'd win as snailmail is a valid way to end any contract in England & Wales (pretty sure its the same in Scotland) but obviously most people don't want to do that. I think the old-fashioned way of describing this sort of behaviour was "sharp practice" 
It was (IIRC) the Daily Telegraph who got Ofcom to open the investigation into Sky which I found amusing.
The Sky 'Trick' is you have to ring a specific number, according to all information you can find. (I am sure it was buried in some T's & C's somewhere.)
This number is of course hard to get an answer on and has a queue of people ringing it at all times.
The normal queuing system does not seem to be working on this number, so you can spend hours trying to get an answer without knowing if you are next or back of a queue of 25!!
(This is based on 'real' experience NOT apocryphal 'Common Knowledge'.)
In reality, you can get through to the normal SKY Support line and be transferred ...... if they are in a mood to do so.
Sometimes you will get the 'Please call this number' script instead.
All this effort is to enable you to 'enjoy' the retention team script to make you stay.
Many people do this every year to get a substantial discount on their monthly outlay, personally I was glad to escape.
