They probably input the wrong status. "Offer declined" seems to me like you were accepted but you decided to decline the offer. I would call the admission office and ask.
They put in the wrong status. I would call AADSAS and have them change it to Application Denied, since all of the schools that rejected me had that status.
Just because a class is full right now doesn't mean spaces won't open in the future. I would call the school regarding your situation. They will be able to offer you the best advice.