Hello and good morning to you.
The simple answer to your question is that someone has to manually block a number in his or her phone. It is not an automatic process. In addition, you cannot accidentally block a number either because there are a few menu steps one has to go through to block a specific number. Maybe someone at your brother's house or someone he may have lent his phone blocked your number. Ask him to check his phone and unblock your number.
Since each phone is different in how the blocking and unblocking process is done, I am unable to give specific instructions that you could pass on to your brother. If he is having difficulty in finding how to unblock your number, tell him to go back to Verizon so that they can help him to sort it out.