Pegasus Airlines Cabin Baggage Confusion on Adana-Riyadh Flight

I recently flew with Pegasus Airlines from Adana to Riyadh, with the Riyadh leg operated by Flynas. My account showed I had cabin baggage for the Istanbul flight, but not for the Riyadh flight. At the last minute, I canceled my cabin baggage allowance. However, when we reached Flynas in Istanbul, I was told I did have a cabin baggage allowance. Because of Pegasus, I went through unnecessary trouble and lost my 8 kg baggage allowance. When I called Pegasus, they said they couldn't provide information about Flynas flights. If you can't provide information, why are you selling these tickets in the first place?