Welcome to the RingCentral Community

If you have the numbers that are calling you can script logic in the call flows in Studio for Contact Center. However, that does not always work since they'll use different numbers.

There are potential answers to you're questions but are dependent on the specific circumstances.

Talk to your Account Manager and possibly speak to Professional Services. YThey can often figure out a custom solution based on the specific scenario.

Apologies there is not an easy answer.

Robocall is indeed a problem in RingCentral. You can find these references

https://community.ringcentral.com/questions/30494/more-than-two-dozen-robocalls-per-day.html

https://community.ringcentral.com/questions/28768/robo-calls-create-extra-expense.html

https://community.ringcentral.com/questions/27003/unblockable-repeat-robo-calls.html

Though I havent found much solution with this within the community regarding blocking but it seems RC product team will be taking care in future verdions as described here

https://community.ringcentral.com/articles/28313/robo-caller-mitigation.html