Sucurri helped me out this week by cleaning up my site after an infection for which I am most grateful. However the support ticket despite having a Reply button goes nowhere, even when I temporarily turn off our 2-factor authentication option.
The only way you can reply back to their support ticket is to go to Products > Website Security & Backups, then manage Website Security which then jumps you over to Succuri's domain.
You then hit reply on the ticket and get to the support thread. I had reported this issue about 4 months ago directly to Succuri and nothing has changed, it still doesn't work, clicking on the Reply button in their support emails won't directly log you into their ticketing system.
Thanks for writing this post! I've sent it to the Sucuri team to review. Take care and hope all is well!