First of all you need a photo and a question. For example: Your ATM fee marked red and the question: “It’s only a machine, why do I have to pay so much for it?” or your mobile billing with the roaming fee: “Why is the same service in another country so expensive?”
Post it everywehre in your social networks and post ist on the #Facebook page of the Company or Brand.
If they don’t anwser to you, then tell everywhere that the customer support doesn’t respond to complaints.
If they answer with their terms and conditions, then tell everywhere that you expect a human customer support and no gibberish.
If they delete your question, then show the screenshot of your question everywhere and tell the world that they violate your right of free speach and blame the #censorship.
If they send you an individual answer, then accuse them, that it takes too long.
Always remain polite but pushy.
Try with naive but polite behavior to lead them to mistakes.
Then you can tell everywhere: “I only asked a simple question but they insult me!”