The phone system works like this: the carer dials a freephone number when they arrive, and again when they leave. So there is a digital record of how long they stay.
My Mum had carers from Sevacare. They were a mixed bag but generally pleasant and capable. She (or rather my Dad) only told the company once that a particular carer was disliked and that carer didn't come again. My Dad let them move on, once they'd done their tasks. Or they sat and had a little chat with him and my Mum. Sometimes they said that they should have been at their next call 5 minutes ago! They were allowed no real time for travelling between customers. I think only once, in 2 years, did the carer not turn up as expected.
I think the problems arise when the customer lives alone. Then the carer is more likely (it seems from the programme) to bother less.
I really think that old, single people who need daily care are better off "in care". Then they have company, meals at the right time, etc. The trouble is, care has been put out to these private companies who are exploiting both the carers and the cared-for. And the boss pays himself millions.
Councils should bring care back "in house". There need to be more council-run care homes, and far more money for funding. Sadly, I don't see this happening but I think it's the only solution for an ailing, ageing population.