How the hell do I get an appointment to register my new car?

I have been trying for WEEKS to get my new car registered/pay sales tax/get plates.

Every time I try to schedule on this link, I get a message saying that there are no appointments available: https://www.hctax.net/Auto/Appointments/Appointment

I have tried every branch withing a 30 minute drive and every date between today and April 15 (when the COVID exemption expires) and they're apparently ALL full.

I tried calling the downtown branch to see if they just do walk-ins, but nobody is answering the phones.