Go to Purchase control and make sure Sequential Receiver number is turned on.  The probelm is that if you do this it locks other records during processing so for example you cannot have multiple people working on receipts/ orders at the same time.  So if you can live with the delay this can cause you can get it to work like you require

Hi Phi. 

Sequential receiver is currently turned on. 

Issue is when doing a cancel backorder a receiver number is assigned, but no record of the receiver number is recorded inthe system.

I manage to replicate this issue and im not sure if this is my design or system issue.

It should not consume numbers.  The receiver is only created when the inventory transaction takes place.  As there is no inventory transaction it is just a cancellation of a BO the number should not be consumed.  Are you using a modified version of receipts?

Using default versions and not a modified version of Purchase Order Receipts.

Not sure why its consuming receiving numbers. 

QAD has confirmed that this is a bug affecting 2015EE. However they wont be creating a patch to resolve this issue but have provided a workarounf which unfortunately due our process, does not work for us.