The the thing to do is go to sentrysafe.com/customercare/lost_your_combination. You must enter the model and serial number. If you registered previously your combo will be there but if not you must get a notarized letter and send it in to receive your combination it will cost you 20.00 and it takes 3-5 days to process. You can expedite for another 10.00.
That is the only way to retrieve your list combination.
You could also try a lock smith that can unlock it at least.