ADP Customer Service Representative (CSR) interview questions

I applied online, 5 days later received an email to schedule a phone interview. Had the phone interview 2 days later with the screener, she asked basic questions about my experience, salary expectation and why I should be hired. That was on a Thursday and the next Monday I received a phone call to schedule a face to face interview with 2 hiring managers. The interview was scheduled on friday within the same week. During the face to face interview they asked alot of behavioral questions and explained about the position. 2 business days later I received a job offer.

I was a referral from a friend. I had 2 phone interview and a 1:1 interview. It sounded like I was an excellent candidate and was told about the next steps and that they wanted to keep me on. I haven't heard from anyone since. I followed up with the 2 recruiter and sent an e-mail to everyone. 4 months later and I still haven't heard from anyone. I thought communication and hiring was their specialty. I'm astounded.