Hi James,
I have purchased several items from C4Depot, including those you mentioned, but it’s been several years so I can’t vouch for their current support. In the past they always responded to my inquiries, though I do seem to remember that it may have taken a day or so at times. Hopefully their lack of a response to you is only temporary. As far as I know, they are just a two-man operation, so they don’t have a dedicated support department and delays responding are somewhat par for the course.
As far as the files are concerned, they shouldn’t just disappear, so it sounds like they may have gotten corrupted somehow. If you didn’t keep backup copies, do you still have the download link (if that’s how you got them)? Or if their online store has you set up an account you should be able to access the downloads there. I don’t remember how that worked as it’s been at least five years since my last purchase.
Good luck.