A call received on my phone which is an automaton ...

A call received on my phone which is an automaton and asks me to call back as soon as possible. When we recall it is also an automaton. And to get someone you need a file number ... But if you don't have one and you don't know the reason for the call, how do you do it?
Epilogue: I ended up having someone "real": the reception and processing of my request was very, very well managed! Thank you :)