My company is asking me to provide the boarding pass for reimbursement purposes. However I used the boarding pass via app and did not printed it out. I've found websites mentioning that it is not possible to recover an old boarding pass.
Can the airline company give me some certificate that took the flight? Is there any other way to prove this to my company that I took the flight?
EDIT FOR CLARIFICATION AFTER COMMENTS:
My company is a University. They say that one could buy a ticket and latter ask for the refund with the airline, and go to the place in a different way, so the purchase receipt does not prove it. The boarding pass should be acceptable, because you take it just after the check-in. They told me without the boarding pass (Delta airlines already told me they can't provide), a Document from Delta, mentioning that I boarded should be enough. Do you think Delta can provide this?