When a C4 explodes, it will degrade or destroy blocks on all of its sides except underneath. Some blocks require more than 1 c4 to get through. For example, a piece of cracked bricks can be destroyed with 1 C4, whereas Iron Plated stone bricks require 4 C4. You can see more about this in the spawn.
If you tell me how you use the C4, I can explain why it didn't work.