My gmail doesn’t receive emails. I can’t log in to my cloudflare account to try to fix this, as I have apparently forgotten my password. And I can’t verify my credentials because that email address doesn’t currently recieve emails due to an MX record problem.
Is the domain registered with Cloudflare or with a different registrar?
If it is a different registrar, you could add the domain to your new account and activate email routing to forward emails to an @gmail address or something.
Your could then use that to regain control over your old account with the password recovery function and change the nameservers back to your old ones.
I probably don’t need to say it anymore, but you should not use an email address to manage an account that is required for that email address to function, or you will run into problems like this.