Managed payment: Buyer opened non received item case 6 months after item was Delivered

[knateb]

Managed payment, This department is never opened, I've tried to get in contact with them for the last 3 days. Buyer purchased a pair of glasses from us 5 months ago. Item was delivered to her and we have proof since item shows delivered with the order number 22-05500-51781 and she left us a positive rating AND she sent a message to us on 8/8/2020 stating she loved the glasses! Now she opened a case with her bank that she didn't receive them! Managed payments put a hold on our funds and has opened a case for her. The case asks for proof of tracking number, as we all know we don't have that tracking number after 90 days. If I don't dispute it what happens since I can't put in a tracking number. In the dispute it doesn't allow me to put any other proof such as the message she sent and positive rating as proof, or the order number which shows deliverd. What are we supposed to do? Thank you in advance for your advice!