Occasionally, I come into contact with people or businesses I don't want to hear from. Sometimes, these people call my mobile phone.
In the past, I would save their number in my phone so that if they called, I would know it was them and not pick up. However, this could still work me up. Leaving them as an unlabelled number wasn't that useful, because, depending on my circumstances at the time of the call, I often pick up unfamiliar numbers.
What I've since done is created a single "Do not answer" profile in my phone, and added all the numbers of people I don't care to hear from again, to this profile. This means that I automatically know not to answer the phone. It also means I have no idea who is calling, so I get far less worked up when the phone rings. It could be any one of a number of people. It is much easier not to care.