air travel – Need to find if an international flight 2 months ago was cancelled

My parents were scheduled on UA8784 from IAD to MUC on July, 24 2020 22:30 and were told it was cancelled due to covid several days beforehand. They were refunded. We were on the same flight but as the Lufthansa partner LH415 IAD (Dulles) to MUC (Munich) July, 24 2020 22:30 and we called to cancel since we already knew the flight would not take off when my parents told us. Now we are told by Lufthansa that we cannot get refunded because we were the ones to cancel and that the flight was on time. How can this be true? The online historic flight data seems to only go back a few days. Thanks!