@Clzee when you place your order via Topcashback it has to track correctly from their site to BT.com for the referral to be paid. When this has happens correctly the order reference will begin AJM.
There are many reasons why the order may not track properly and Topcashback have guidance on there help pages for assistance with this. If the order hasn't tracked you will need to take up your concerns directly with Topcashback customer service.
@Clzee The Z order reference is the code you get if the order was placed directly on BT.com. Regrettably if it hasn't tracked correctly BT can't help you as your cashback agreement was with Topcashback. I'd recommend you follow their escalation process to progress your complaint with them.