I'm not sure if this is the right place to post this but I'm totally lost and I have no idea what to do about this.

I bought my domain and hosting package with ValuableHost.com 4 years ago, but changed my hosting to another company after a month due to finding a better (*ahem* and more reliable) hosting company.

Things have been totally fine since then, my new hosting company is still amazing but I recently needed a backup restore and I had to be moved to a larger server because the one i was on didn't have much space left on it. So now I need to change my DNS and i can't because despite the site - valuablehost.com - still existing, when i log in, I can't access the details to modify them. So I figured the easiest thing to do would be to change my registrar to the company that hosts my site, but I how can i get an EPP code from a company that doesn't even seem to function anymore? They do NOT reply to any emails (and i have sent more than a few).

I have no idea what to do so any help would be greatly appreciated.

Check who is the Registrar of your domain, talk to them.

Well, it says ENOM on my whois but when I ran a search on their site, it said it was through one of their resellers (domaincup.com). When I tried to contact domaincup with the provided email address, the email was sent back to me with a message saying "This address no longer accepts mail."

You can contact ENOM directly, see if they can help you.

Call enom (phone number on there support page). They will give the reseller 24 hours to respond then email the information to registrant.

Also, after that 24 hours enom would probably just let you transfer the domain into your own account.

Yep. Call eNom. They will help you. But I'd advise against putting you domain with your current webhost. Your example is just one of many things that can happen to lose control of your domain. Put your domain directly with a registrar.