Then go back without the bottle... they can look up your last order and RX. (most pharmacies now scan a copy of the RX into the computer and they can look at that, to see if the correct amount was ordered and entered).

So you use 120 a month? And you probably got 100? This means either
1) Maybe your doctor only ordered 100? and you should have 120?
2) they filled RX with 100 ct bottle and the tech forget to add the 20 extra in that time
3) they ran out and forgot to give you an owe slip
4) they typed in the wrong day's supply so insurance declines to pay

Wherever the oversight is, they should correct it so you do not go without medication. Using an automated feature, will not often give you information right then. Most pharmacies will however CALL you back later when the claim is denied, or if they are out of medication. The fact that they did not, leads me to suspect a miscount is where the error is. They assume you still have pills and are requesting early. They do not know you are OUT.

You have to take the next step. If you cannot go in, then try and get this fixed over the phone. Talk to the pharmacist and not a tech. If you have someone else pick up your medication, they can fix the issue with you on the phone.

There are many many details involved in filling prescriptions. Things happen, and a good pharmacy will fix any problem quickly for you.