My exp on applying to Cov is really frustrating, no replies from uni at all

I'm applying for a top-up undergraduate course as an international student. The experience I got applying to Coventry really frustrates me.

Normally you apply through Uni's own portal, but I found the course was not listed in the system, so I sent an email asking if I could apply through UCAS as an International Student. NO REPLIES.

Then I started my application on UCAS, found that course and submit as one of my choices. The next day, received an email from Cov uni informing me that I got the offer, however, it is conditional with lots of documents to be filled in and sent. So I wrote them another email asking how I send them my papers. NO REPLIES.

A couple of days later, I thought that maybe I need to make firm choice on the offer so Uni would send me the link to the uni portal about uploading those papers. So I did, and nothing happens since then. I sent multiple emails to different addresses (ukadmission, international admission, etc) asking how can I make the change from conditional to unconditional and eventually a CAS letter. Guess what, STILL NO REPLIES.

Meanwhile, I tried livechat and straight dialing. You guess it right, no agent was available and no one picked up the phone.

I'm totally lost now, what should I do?