Some pharmacies just flat out lie to you.
When I had my adderall script, I got it filled every month at a CVS since they were cheapest and every month was a circus. I'd come in and try to get it filled, and they would look in this folder(not the ACTUAL stock or even the computer), and say it's out. And even refused to keep my script, and fill it when the new order comes in, nor tell me if any other stores had it. And calling them on the phone and asking is a joke.
On several of these occassions, I waited for the next shift and magically it was in stock and would get it filled.
I don't know what their protocol is, but it's really strange.