Doubt regarding flipkart invoice

 I want to exchange my mobile in flipkart.

let say 4000 rs.

but on delivery it price drop because of defect.

Orginal = 12000 -4000 =8000

but now =12000-1500=10500

i pay remaining by cash.

Now my question is how invoice will given

means it will original or it will based on adjusted amount.??

CAN ANYONE  ( SIMILAR SITUATION ) could share their invoice to me.