I think you can use LEO Privacy to try to block unwanted calls. Harassment Interception function is very nice and works well. Highly recommand it to you! LEO Privacy Applock Hide Safe Android Apps on Google Play
Blocking phone numbers depends on careers and phone brands, many brands come with options that can block only a certain number while some carieers can let you bar all call. Based on your request you want to block on a single number so you will need an app like black list or call manager. you did not specify you make and model but make a seach for blacklist for your model or call manager for your model.
Answers & Comments
I think you can use LEO Privacy to try to block unwanted calls. Harassment Interception function is very nice and works well. Highly recommand it to you! LEO Privacy Applock Hide Safe Android Apps on Google Play
Blocking phone numbers depends on careers and phone brands, many brands come with options that can block only a certain number while some carieers can let you bar all call. Based on your request you want to block on a single number so you will need an app like black list or call manager. you did not specify you make and model but make a seach for blacklist for your model or call manager for your model.