That’s your booking reference, the OP was referring to their account number which is in fact your P & O Loyalty number.
Ours is on our booking confirmation under the info about the cruise as below:- on the same lines on the opposite side of the page is the pricing info.
Title / Last Name:
First / Middle Name:
Age at Sailing:
My Account Number:
If you haven’t got your P & O booking confirmation and only your confirmation from your TA you need to ask your TA for it. If the account number isn’t on your booking confirmation then query with your TA or P&O if you booked direct, but as suggested it might be you haven’t yet qualified for the Peninsular Club as haven’t yet sailed for 15 days. You have to have actually sailed and not just booked to qualify, but certainly query it.