Twilio has a call blocker feature called NoMoRobo, which would enable all GHl accounts to automatically filter and block junk calls based off of a near real-time master spam list.

You can look up the rest of the features on NoMoRobo.com, but Twilio has their own case study on it on their website (https://customers.twilio.com/en-us/nomorobo). You can make this a per account or subaccount basis, but this is the fastest way to help alleviate the monthly burn on the accounts with wasting minutes and time on junk leads.