I am not saying that you made the same mistake but it is not enough to set the right frequency, you also have to press the correct transmit button. As per the manual, p. 256 (upd Dec. 20th 2024):
I wanted to scream here in the forums: the tanker doesn't work, it won't respond! my wingmen doesn't comply and doesn't answer! Not even the tower is answering! Wtf!
No, it was simply my error to only press [\]. Once I used the correct transmit switches, my wingman (wingwoman?) engaged like a proper fighter pilot (and much better than I did).