Windmill Strategy Web Designer interview questions

Was told during the interview process that I would 100% be making it to the next round, and it was a good conversation. However after a week I got an email that said they were going slowly but reiterated in writing that I would 100% still be invited to the next round...and then a week after that I got a rejection letter. The interview itself was fine, but it was a bit unprofessional to promise, in writing, the next stage when obviously they did not follow through.