Hosting our free subdomains with other hosting provider is not possible, or at least it’s not supposed to be.
Perhaps you were able to do so before by exploiting a bug in our platform. But then if the bug is fixed, it may break your workaround.
If you want to host your website on a rf.gd subdomain, you must host it with us (or with iFastNet). If you want to host it with Amazon instead, please get an actual domain name for yourself that provides this ability.