Some pharmacies have a connection between the sale register and the RX history. Every so many days, a report is generated to show what is not picked up (meaning not scanned out at the register). Rxs in those are scanned into the register as a rule. Not all pharmacies have this tho. When these reports come out and it shows 3 days remaining or less on certain orders, then the techs call the people up.
It exists because there is a 7-10 day delay in billing the insurance company. If you do not pick up the RX when it is filled, and the 10 days go by, the insurance is billed for it. Years ago there were law suits against Walgreen's and CVS for this. It was called insurance fraud. But in many cases it was just not picked up. Now most chains have elaborate checks to make sure RXs not picked up are cancelled before the billing goes thru.

This sounds like what is going on with you. But I will say...
that controlled substances are always picked up unless the patient goes into the hospital or dies. People as a rule never forget to get them. Other things however, even antibiotics are sometimes not picked up. You'd be amazed!