iphone12 does not buzz front entrance door

I live in an apartment building. with my old phones when someone rang my buzzer number my phone would ring, I could talk to them and buzz them in by pressing "9". No App required. Never had to set my old phones whatsoever.

Now purchased Iphone 12 about a month ago and ever since when someone rings my buzzer, I can talk to them but door will not open when I press "9". I didn't change my Ph#, Building management doesn't understand the problem. Frustrating.

Would it be in my settings, or what could it be?

I already regret buying an Iphone!