Pegasus Airlines Customer Service Nightmare! Denied Boarding, Lost Luggage

I was supposed to fly to Dusseldorf airport with my sister today. However, Pegasus company didn't let me on the plane because I hadn't checked in online and claimed my name was on the reserves list. Oddly enough, I've flown without online check-in before without any issues. Even though I explicitly told the officer that my sister could take my luggage, it didn't arrive, and we have no idea where it is now. Additionally, a portion of the ticket fee, which was supposed to be refunded, was deducted due to a tax deduction. I didn't receive any service, and the money I paid wasn't fully refunded. Passing through passport control, the police control process took quite a long time before I could return, and I spent almost a day dealing with these procedures. I definitely do not recommend this company to anyone.