Missed my flight because I didn't get e-mail with boarding pass [closed]

This must be the weirdest "missed the flight" situation ever. We were four, traveling from Alicante to Keflavik. I checked in online with the app and got "you are now checked-in" and allocated seats 20E and 20F.

When we arrived at the airport, it said "boarding" and the woman at check-in says the flight will leave 30 minutes earlier and we should have gotten an e-mail about it. None of us received any email. She tells us the check-in process has closed and tells us to rush to the security line and scan the online check-in code. There, I realized I never had any email with a QR code.

After some fuss the staff says, "Sorry, you are stuck in Alicante." The strange thing is that there was a 30-minute delay, but not a 30-minute earlier departure time. Is the airline to blame or the airport?

EDIT:

Departure time was 01:05 - We were at the airport 23:45 - at the counter 23:50 - There was a line - the last people in front of us was having some trouble and talking to the woman at the counter - After 10 minutes we asked where they were going - Appeared they were on a totally different flight - Than we talked to the woman at the counter and she said "why didn´t you come in front of the line before" and told us check-in was closed.... She told us to run to the front of the security lane - our two friends had QR code and it was scanned - When I opened my app the QR code was gone - tech error...