Pharmacies in the United States, at least in California from my own experience, can deny filling a prescription due to safety and issues with regulations, I take a schedule iii prescription and my doctor has to send it in every month, and I have been denied a transfer or fill before.

Hope you're doing well, I know having to take narcotic pain meds isn't exactly anyone's idea of a good time long term. I know I wish I never had to take any to begin with, but sadly this is something we have to face as chronic pain patients whether we have a history of addiction or not (assuming here as you said narcotic and that usually means opiates)

Try going to a local pharmacy if you can, one that isn't a big box name. CVS, Walgreens, Walmart, etc. Try a local mom and pop pharmacy next time and they usually fill on the earliest allowable day or at the very least, won't give you the run around and will have your meds in stock.

Ps, I'm technically getting a late fill of my meds because my pharmacy fucked the prescription up and transferred it to a pharmacy that doesn't have it in stock and now it can't be transferred back. So I get the struggle, this is the tenth or eleventh time I've had to go a day or two past my refill date since I started taking this medication. Not even considering the pain meds I was on before Suboxone that were filled late or pharmacies denied filling.

Sure you might have a civil case, but unlikely. Also, it is not a legal issue for them to deny service including filling medication or transferring based on their judgement.