Bringing up this thread because I had to book a Transavia flight for later this year.
When booking, and in the confirmation email, KLM stated that I could have 2 pcs of cabin luggage (max weight 12kg):
1 hand luggage (max 55 x 35 x 25 cm | 21,5 x 13,5 x 10 po ) + 1 accessory (40 x 30 x 15 cm|16 x 12 x 6 po )

Today, I got an email "reminding" me that only 1pc of luggage is allowed, and that the size should be no more than 40x30x20 cm so that it can fit under the seat.

I'm puzzled by the conflicting information... especially since I chose Transavia over Easyjet for the promise of being able to bring a small suitcase. Any feedback on the actual current policy (its implementation being a different topic)?