Learn how to set up separate call setting for both the SIM's.
Applicable for ColorOS 5.2 device. Check your ColorOS version in [Setting] > [About Phone].
What is separate call setting?
ColorOS 5.2 gives you an opportunity to manage and set your two SIM's separately. Block calls, block messages, blacklist and blocking terms can be managed on your will.
Steps to use separate call setting:
Go to [Setting] > [Call] > [Block] > [Block calls] > SIM1/ SIM2