AT&T Senior Associate Quality Assurance Engineer interview questions

I had an interview around mid-September and was told that I performed well. However, I never received any update or feedback from HR. Even after multiple follow-ups through my referral, there was no official communication about my selection or rejection. Later, I found out they had already hired someone, but again, no one from the company informed me. Recently, after one and half month they even asked through my referral if I could join within 15 days—without giving me any offer letter or direct contact. This kind of unprofessional communication and lack of respect for applicants’ time is disappointing.