Hiring Freeze/Unresponsiveness of HR

I have been going through different stages of the selection process for the DAA role at ZS, with a referral. After clearing all the rounds, which took about 2–3 months, I recently had a final CTC discussion call with HR. After finalizing the offer, I was informed that I would receive the offer letter between March 5–7. However, I haven't received any response from their side yet. I have tried reaching out via email and call but haven't been able to get a response. I am unsure whether this is due to a hiring freeze or some other delay. If anyone could help, I would really appreciate it.