It is great that your cat recovered; so you can say no to convenia in future! It really is an awful product and many cats died from it. And you are so right one has to be extra vigilant when going to the vets. It is best telling them you want to discuss every treatment in advance and ask for...
Soleya, so sorry for your tragic loss. This vet wronged you and your cat very badly, his behaviour is utterly irresponsible. I can imagine pain and sorrow you are feeling as I went through a similar experience last year. You need to allow yourself time to grieve, it cannot be helped how one is...