Federal-Mogul Graduate Engineer interview questions

I was contacted by the HR department one month after I applied online through Federal - Mogul's website. They did not let me know beforehand that I would be having a telephone interview so that was a bit unexpected. The questions at that stage were mostly motivational (e.g why I applied for this role etc.) and competency based. The company representative asked me on the phone whether I would be available to attend an assessment centre on either the 5th or 12th of April 2017. I specified that I would only be available on the 5th of April but it seems that this was not taken into consideration when I received an invitation for the 12th of April (passed the telephone interview). I replied back to their email politely asking whether a rearrangement would be possible or otherwise I would have to reschedule my flight tickets to attend the assessment centre on the 12th. As they would not respond, I also tried calling on the HR coordinator's phone and left a voicemail but I never got any response. Instead on the day of the response deadline, I received an email saying that my application is withdrawn. Even after emailing my complaint to them about this incident, I never received a reply. I've attended assessment centres in the past but never have I experienced such an unprofessional behaviour by a company. What a horrible HR department with very poor coordination and organisation.