How to ignore a call?
Macrodroid , easy to learn automation app can help you

You can create a macro as below to


Reject calls
Create customisable SMS to let the callers know reason for rejection





To activate the macro you have two choices :


In Constraints add the condition you want the macro to run, like day of the week or time of day
From the app widget . Select the widget, drop it on to your home screen and assign this macro to the widget. You would then be able to manually enable / disable the macro if the earlier option is not suitable


To understand how MacroDroid works and required settings,  my answer here