UPS complaint: Lost Package

I shipped a package with Shipment ID MAS357BBE203A with UPS on December 8th, 2021, from Niagara Falls Canada heading to Irvine California. I could track it till it got to the US customs and released from there. However, there was no update on tracking information from that point. After several weeks of follow ups and contacting UPS to locate my package I was told that my package has been lost and they are unable to locate it. I really would like to know how a 44lb package could get lost! It is hard to believe that UPS would misplace such a big and heavy box. I believe the package has been opened and the contents were taken since it contained Serengeti sunglasses which interests most people. But along with Sunglasses it contained some books and personal items that has high sentimental value to me and cannot ever be replaced with money! I want to know what happened to my package and where it is! Your apology and excuses do not replace my personal belongings. Find my package and send it to me!