Almost certainly a glitch. In the main thread about the promo, someone posted this:
"Wow. These guys are terrible!
This morning I logged in to check my balance and I was told my username and pin was not correct (it definitely was correct, I’ve logged into Iberia enough times over the last 5 days or so). Called the service centre and they told me that my account must have been deleted because I haven’t used it in 4 years. I said that is not possible since it was created in June 21st, 2018. She said I have to email them to get it resolved.
Anyways, I hung up and called back and got the correct answer from the second agent: some of their systems are down and many people have called in with the same issue, try again in a few hours.
Anybody else getting this issue? My girlfriends account is working just fine, but mine is locked out."