Years ago, and with previous cats, I asked a friend to feed them while I visited mum for a few days. He was a dog person. When I got home there was masses of stale food left in their dishes. Luckily the cats were okay. I think he was so used to feeding his dog that he didn't realise that cats don't eat german shepherd size meals! This was inspite of the fact that I had TOLD him how much to give them, and to throw away anything they hadn't eaten the previous day.
From the website, it seems that they are mainly dogwalkers.
One thing which occurred to me while reading the thread was: could you report them to the dreaded RSPCA? Effectively, they've been cruel to your cats. Problem is, would the RSPCA get the wrong end of the stick and blame you! These so called animal sitters shouldn't be in business.
When you go away again, get a recommendation from your vet for a CAT sitter. Are there any friends or neighbours nearby who you trust and who are cat people?
I hope your pusscats recover soon.