There is no secret here.
You've just experienced three more customer gripes:
Gripe #3: Customers hate getting the run around.
Fix problems. Quickly. The first time. Don't make customers jump through unnecessary hoops.
Gripe #4: Customers hate being sold to when you should be helping.
Knock it off with the sales pitches. Cut them out of your hold music. Stop upselling on service calls. Just help your customer. Then, and only then, can you think about selling again.
Grip #5: Customers hate being lied to.
This one should be self-explanatory.
You've now made it through my blog post of customer horrors. I'm betting few people will make it this far.
And, you've discovered the real secret to diffusing angry customers - empathy.
You know what it's like to be in their shoes, so you're better able to demonstrate to customers that you understand and care.