Intra European flights never have a bigger seat in business, always same seats throughout the cabin, it is only about more legroom and only for some airlines (and middle seat free if it is a 3-3 configuration).

I had a similar issue this summer with Lufthansa, that as part of a business class trip with multiple segments booked me and my family on one Brussels-airlines operated flight that only had economy class. We had zero business services (no priority boarding, no lounge, had to pay for seat, etc) and both airlines point at each other for any form of compensation so we've got nowhere. It is very possible that AF sold you an economy-only flight as business as Lufthansa did with us.