Atos User Experience Designer interview questions

The FR and interviewer was not professional at all, right after the interview, they told me: you gonna get the job, and the HR even send me an email which said: “ the interview went very well, and we would like to proceed to an offer!” I regard this as an unofficial offer, however, after three days, they told me they had made a last minute change! I highly suggest the company to be professional at your interviews, do not give any oral offers before you made your final suggestions. A big as Atos, really shouldn’t make stupid and unprofessional mistakes like that!