Unable to unlock Mac mini; Locked Via Find My iPhone

I locked my Mac Mini. I have retrieved it and I’m ready to unlock it. However, there is no “unlock” option in the Find My app or on the iCloud.com/find website. It keeps asking me for a numerical code to unlock the device. I did not assign a code when I locked the device. If I had it would be one of the few that I use or a variant of said codes. I’m 100% sure of that. I purchased this Mini in 2017. I have not and don’t want to erase the device. I cannot find proof of purchase other then a bank statement for an amount at an Apple Store. Is there another way to unlock the mini and/or will the bank statement suffice as proof of purchase?