Ryanair complaint: online check in system doesn’t work

On February 27th around 8:30 pm I checked in on Ryanair app for my flight
Stuttgart-Niece on February 28th at 6:20 am.

I had a hard time with the app, it took me several attempts until I finally was able to insert all the info despite the app freezing again and again.

The next day, though when I got to the airport I was told I did not check in online and I was supposed to pay 55€. I insisted saying I had checked in online the day before. I was told “No you did not”.
That was not a pleasant customer service, to start with.
Then the same lady told me to try again and check online since it was still 1:30h before departure.
This was the wrong information because I was unable to check in.
Later a second staff member informed online check in worked up to 2:30h before the flight.

I had to pay 55€ When I had done my part on time.

The same thing happened to another gentleman checking in at the same time.