The idea that there is a registry is an idea that is spread by folks who just want to make money. There is no such thing. I am sorry that someone got your $300.

Service dogs are treated differently under the law. They are generally allowed any place that the public is allowed, but the animal (almost always a dog) has to be trained to do a specific thing that mitigates the owner's disability. There is no registry for service dogs, either.

Emotional support animals support their owner simply by being present. So if petting your cat helps you feel less anxiety, it is an ESA. If your cat is trained to go get your Xanax when you have a panic attack, it is a service animal.
Depending on what is going on with you, you might be able to legitimately train your pet as a service animal. My dog is trained to alert me when I dissociate, so he qualifies as a service dog.
I'd be happy to try to answer any questions you have on the subject.