Ok, the post office(parcelforce.com) emailed me back:
Thank you for your email.
I am sorry to hear that you are still awaiting delivery of your item and can understand your concern at the delay.
I have checked our records and we are unable to deliver your parcel due to problems with the address this is due to the PO Box address, we do not deliver to PO Box addresses we do need the full address and post code.
So what I have to do now:

How the PO BOXES work? Fedex cant deliver, UPS cant deliver, the National Pos Service cant...
So sad....
If they send the package back...and If I send it back again to the Agents United this time...I have the guarantee they are going to get it?
HELP
