This is truly heart breaking. I'm so sorry for Dani. I'm sure he was beautiful and like every cat most deserving of love and care.
So you live in Cairo, Egypt? I have to point out the irony of being now so fricking cruel to cats when in ancient times they used to worship them
Anyways back to Dani what kind of vet marries a cat poisoner? The kind that sees animals lime objects that provide an income.
Nothing can bring Dani back now however since you care for cats like I do start looking for groups of people that share those feelings and rescue cats. I can assure you people like you (and people like in these forums) are everywhere, even places that seem unforgiving and uncaring have gentle hearts that love them I have no doubt about that as I came to know rescue groups in Mexico with lots of people that put all their heart in it.
Find them on Facebook or online and when you do ask them about a decent, honest vet that doesn't see them as "things" to profit from.
Needless to say not to go back to that vet. No cat should die over a microchip implant.
I'm honestly so sorry about Dani. it sincerely saddens me. Don't blame yourself. You cared for him and you were both victims of negligence.
RIP little angel Dani