I agree with the other posters. I would call the pharmacy and see if they will call or fax the Doctor's office about the mix-up. They should be able look-up their records and see that your son had a prescription filled on the day in question. There has to be a way for them to clear this up. My family has all their prescriptions at one pharmacy and nothing like that has ever happened. So, it may be time to consider changing pharmacies as well, that just seems ridiculous and terribly unprofessional.
I hope this all gets sorted out.
~ Fiona Jo