Asking question in middle of active rasa form

Question

I have a rasa form that asks for email, phone , username , name and signup related details. I also have an API that checks if the phone and email exits or not, if they exist it returns a list of users containing the respective details. Now after getting email and phone from users, I want to give that list in form of buttons in rasa and user can choose either of the users provided the that list of buttons. I managed to create the list using dispatcher.utter_message(text="Choose User",buttons=buttons_list), but the list came as a message and not as a question and I was directly asked for the next slot. How can I manage to do this kind of thing in rasa. For reference I am putting the content of my domain file.

  email:
    type: text
    influence_conversation: false
    mappings:
      - type: from_text
        conditions:
          - active_loop: registration_form
            requested_slot: email
  phone:
    type: text
    influence_conversation: false
    mappings:
      - type: from_text
        conditions:
          - active_loop: registration_form
            requested_slot: phone
  username:
    type: text
    influence_conversation: false
    mappings:
      - type: from_text
        conditions:
          - active_loop: registration_form
            requested_slot: username