Unfortunately I haven't solved anything, it seems to be back, at this point I don't know what to do....
Here's a quick checklist to go through...
You must be registered to see the links
Unfortunately, due to the 'nature' of your website, if you get to the point of 'arbritration', you may run into DMCA issues...
I'd suggest checking your email account that you used to register the domain, and change the password with something very strong, and probably 2FA the sucker to boot. If you have a separate computer/laptop that isn't on your local network (if you have several computers linked via ethernet or whatever) use that one to access your email account when you do the change, that way if there's any spyware on your server system, it won't see you do the change... if your internet router/wifi is infected, that could still be an issue though.
I'm sure there are smarter people than me that can walk you through some of the other stuff to check. I'm just guessing in the dark here.
The next thing you could do is snag a new domain name and use it instead, until such time as you've fully locked down 3dload.net again. Again, though, if you have spyware on your local network, that needs to be found and destroyed first.
If the PC or Laptop you use has been connected to your server (I'm guessing that you have a local server, and are not using a server provider), well you don't really know how deeply the intrusion into your networked computers has reached. Worst case, you could go buy a cheap laptop at Walmart or whatever and use that to 'lock down' all of your accounts remotely, until such time as you get a chance to check your server for hidden malware, etc. Of course, if a new computer (even a cheap one) isn't currently within your budget, well it was just a thought.
I'm assuming you already tried customer support over at Namecheap again, couldn't hurt to try them again.
Again, I'm just throwing out ideas here. I'm sure that others have better insight as to how to proceed from here. Very few things are as friggin' annoying as hijacked domains...