Radio Station not bringing dwellers?

Radio rooms have a very low chance of attracting new citizens to your vault. This is offset by the fact that the citizens the radio room attracts are already adults who wouldn't consume resources without providing a benefit in the same way a child born in the vault would.

Even when having radio hosts with charisma in the 8-10 range it will still take about half a day (or more) for more wastelanders to come to your vault. It is possible for them to arrive in groups of two or three, which is a boon.

The fact that you have not seen any new dwellers after two days while using radio hosts with high charisma and and upgraded radio room means that you are either have encountered a bug and the radio room is not working as intended or your vault is at maximum capacity and new vault dwellers cannot be added. I believe this is more likely to be a glitch because when at maximum vault capacity new wastelanders will queue at the entrance to the vault but will be unable to enter - rather than never appear at all. Consider destroying and rebuilding the radio room to fix the glitch or find alternate means to increase your population.