May I ask if you don’t know the email for the “old CF account” or are you still able to login to your e-mail and manage it, or you also lost access to the email? 
The only way you’ll be able to regain access is by having access to the email address of the account.
These links may help, but they only work when logged out
If you know the email: https://dash.cloudflare.com/forgot-password
If you don’t know the email: https://dash.cloudflare.com/forgot-email
If you know the email and have 2FA issues, follow the process here: Two-factor authentication · Cloudflare Fundamentals docs
May I ask if you’re still able to manage the domain name within Namecheap domain registrar?
If yes, then you can:
- Create a new CF account and verify it → Create account · Cloudflare Fundamentals docs
- Add this domain as a new zone → Add a site · Cloudflare Fundamentals docs
- Change domain nameservers at Namecheap to point to the new nameservers assigned to your new CF account → Change your nameservers (Full setup) · Cloudflare DNS docs
- Add backup CF account as a member → Manage account members · Cloudflare Fundamentals docs
If you cannot access neither Namecheap using below help, I am afraid you’re out of luck here.
The stated domain isn’t even using Cloudflare nameservers:
dns53.cloudns.net
dns52.cloudns.net
dns51.cloudns.net
dns54.cloudns.net
Related to the domain name which you’ve added, if you plan to host & serve videos over a proxied 
domain, you’d be violating the ToS, therefrom you’d have to use Cloudflare Stream for such case.
You’ll need to follow these directions here:
If you already have a ticket, Support will respond to you on that ticket. Questions about billing will need to be resolved by the Customer Support team and cannot be resolved on the Community.