You can directly call 1 1 185 or 95580 to make a complaint.
Because the procedure of closing the account is complicated, the salesperson thinks you don't need it, so it's simplified. Just cut it with scissors and throw it into the trash can. There was no real cancellation. But it doesn't matter whether the account is closed or not, just don't use it.
PS: The teller's behavior completely violates the regulations. You can complain and ask to see the receipt of the account cancellation to prove that you have not signed to confirm the account cancellation.
In fact, the card is not really cancelled. You can still find the card information on the postal terminal system with your name, which is no different from throwing it away yourself.