There are a lot of people who follow protection methods and yet they get affected. Then they wonder why they got affected. What is meant by protection must be understood. If people wear warm clothes during the winter they are protected from the cold, but that does not mean they become immune to the cold. They will still feel cold. However, if they did not wear warm clothes at all, they could die. Similarly, protection methods cut down on the degree to which a person will get affected immensely, but a person will still be affected.
There is nothing that offers 100% protection from black magic except a Taweez, and even a Taweez does not offer protection from black magic done on food and drink. It only offers protection from aerial attacks.
Concerning wearing a Taweez for protection from black magic, please make sure you get it from an Amil who is either well known or who has been proven to have helped others. Do not visit people who advertise and do not pay outrageous amounts. An Amil will ask for money since musk and zafraan are used to write them, and musk in particular is very expensive, but the money still has to be within a limit. There are a lot of frauds who pretend to give a Taweez and ask outrageous amounts so please make sure you do not become a victim.