Apartment gatebox not directing calls to my phone

I live in a gated apartment where we provide our phone numbers and they will give us back a 3-digit code. This code should allow guests to key in the 3-digit code from the gate's keypad, and a call will be redirected to our phone, we then should press 9 to open the gate. 

When I tested it, the gate responds that ‘the call could not be completed as dialed.’ 

The manager at my complex has deleted and re-entered me into the system 3 times and that has not worked. They spoke with the gate company and they claim everything is fine on their end. They suggest that this could be a carrier issue. I troubleshooted with my carrier and they didn’t find any issues on my end.

I have an iPhone XR (not sure if that matters here), but maybe there’s an issue with my phone? Has anyone else had this issue and got it resolved?