What is the best way to handle the angry customer ?

Take the HEAT: H>hear what she/he is saying and never interrupt, E>empathize,  put yourself in his/her shoes and don't try to justify, A>apologize sincerely, T>take action and own the problem. 

This is how you handle an angry customer:

Listen carefully to the problem

Give them your undivided attention

Diffuse their anger by sypmathizing (ie That must have made you feel terrible!)

Be understanding (ie I can see how this is upsetting)

Acknowledge that they have the right to feel how they do

Apologize (they will continue to be upset until they hear an earnest apology)

If everything else fails, offer to call in the manager for further clarification

first you should calm and greet the customer, then ask the customer what is the problem, then tell the possible solution and after that apologies for what happen

Reduce the value of his invoice always, but it should not affect your profit.

Ignore Him in a good way and lovely attitude and tell him everything gonna be alright just like the way he wants it to be and believe me he will shut up 

Whatever he is saying or abusing, you have to just listen carefully and figure out the problem, then try to calm him down as much as possible, try to find a solution for his problem if it's under your authority, if not, take a permission from your head of department to handle it.

empathize them show sympathy and give a win and win situation