Do not "pitch the gatekeeper." They are not qualified to make a decision.
Newbies view the GK as adversaries but this just persists the attacker-defender setup. View them as helpful, and they will begin to be helpful.
I work with many bricks-and-mortar businesses, and their salespeople lack even two basic skills they really should have:
1. They don't know how to get the decision maker on the phone
2. They don't know how to start the conversation with the DM correctly so that there is a "rest of the call."
So it's not surprising that people are having trouble with gatekeepers.
Being desperate for a sale is a bad place to start. Your voice makes it clear to the GK that you are a salesperson, and paradoxically the more you want to talk to the DM the more difficult it's going to be for you.
Take all the tension out of your voice. You'll get much farther. In fact, that tip will get you farther than any technique I could give you.
Start thinking of yourself as a CEO, president, owner. You are one top dog wanting to talk to another. We get to speak with those we sound like. If you don't sound like the top dog, the GK isn't going to feel comfortable connecting you.