Aegean Airlines Baggage Policy on Izmir-Athens Route Cost Me Extra

I want to address an issue I faced with Aegean Airlines on my Izmir-Athens and Athens-Izmir flights. Traveling from Izmir to Athens, I carried a backpack and a cabin bag without any extra fees or warnings about carrying only one item in the cabin. However, on my return flight from Athens to Izmir, I was told at boarding that I could only bring one bag into the cabin and that my backpack was considered an additional item. This information was not provided when I checked in, even though my ticket was reviewed, and I was directed straight to the gate. I was then charged an additional €50 for my second bag. If I had been informed earlier, I could have purchased extra baggage allowance. The staff only checked the baggage of two passengers, ignoring the rest, and almost everyone on the flight had at least two bags.