i would say to dd " i called the mobile number in your phone for that guy - the one you have called 33 times and i spoke to the man who answered the phone about this situation. (its true, no need to tell her what was said!) i want to hear everything from your point of view. if what you tell me does not match what this man has told me, i will take away your phone'"
a bluff! that way, if the guy lied to you, she might tell you the truth, thinking you already know and fearing the loss of her mobile. and if she just left 33 messages but got no call back, then you know he is probably telling the truth. you will also know if the guy she met on the train is calling her (maybe number withheld)