Review Failed Delivery - Uncontactable

I was not home the day they delivered my sss cheque and provided me a registry notice to claim it at the post office which didn't have an address or phone number to call and the delivery office noted it was not even clear (had to guess what CPO meant). I went there and the clerk told me the cheque was not with them but with the delivery man. She gave me his contact number but when I called, it said out of coverage area or unattended. I never was able to get thru the deliveryman even, days after. Now, I have to make another trip to the post office to check if it is now available to claim since their phones aren't even working.