Required Prompt to Stop Robocalls and Telemarketers

We are a wellness center with 3 locations in San Diego. All 3 locations have different phone numbers that customers call even though the calls ring in all 3 offices simultaneously.  I would like to enable a greeting that requires callers to respond to a command prompt to type or say a particular number before the rules take affect. 

The issue is, currently it is my understanding that you can only have a prompt when callers dial the main company number so this feature won't work when they call the other locations.  My goal is to have an outgoing message that says something like, "Thank you for calling DREAM Wellness... if you're calling to schedule an appointment, press or say 5. If you are calling for any reason other than patient care, please say or press 6."  If they don't press any button, I want them to either get stuck in a loop or be disconnected.

If figure this would make the robocalls go away and for the live sales people, they would have to press a button which would limit the amount of calls my receptionist has to answer. Right now we get about 15 sales / robocalls every hour and the receptionist has to stop what she's doing to answer every call which is making it impossible to conduct business.