How to make community gate access work?

My community gate has one of those dial access boxes for the front gate. When a visitor enters my code, it will dial my phone number. I was directed by my community to press '9' to open the gate. It is not working though. It will call my phone, and I can dial numbers, but when I press '9' it just makes a dial sound. Some people say to turn the cellular LTE to data only, I have tried this and it did not work. I have an iPhone 6s Plus that used an iCloud backup from an iPhone 5. I believe the company that makes the dial box is called Linear. I know that it has worked in the past, but it may have been with my iPhone 5. How do I fix this?