HRT should absolutely be covered by any insurance. There's no reason for it not to be. If for some reason it's not, call and talk with them. Talk with your physician and let them know you're experiencing difficulty securing insurance coverage for the HRT they're prescribing -- ask them to adjust their coding accordingly to allow you this coverage.
HRT, FFS, and SRS have all been agreed upon as being medically necessary. It's unfortunate that we have to put up with insurance companies and misinformed/apathetic physicians and surgeons denying us the rights to our healthcare.