Answer:
I have experienced three poor customer service as a customer. They are (A) Use of negative language (B) Unresolved Complaint (C) Unfulfilled promise.
Explanation:
To start with the use of negative language, I was once on a call with the customer service of my Pay-TV over issues of channels not being accessible even when I had an active subscription. The manner which the customer care representative responded to me gave the impression that it was an issue they might likely not have a solution to because she wasn't assuring me of a possible way out.
Also, I have once put across to my web hosting company over issues of persistent downtime. They told me it had been resolved but the reverse was the case. I had to place several calls before they finally got my website live again.
Last but definitely not the least, my internet provider promised to refund my money for a failed data subscription but they never did even when I had made it clear that I was no longer interested in their service.