Paypal — i did not g8et the cashback i was supposed to get in my first paypal transaction

Hi,
I booked a ticket on 16/01/2020 through my sister's paypal account through www.abhibus.com as i was supposed to get a cash back around 500 inr. Again i did not get any cashback.
Registered email id - '[protected]@gmail.com'
So finally i tried contacting the support team of paypal, they said in both the transactions i have made the payment through a virtual card that is completely untrue. So i am not eligible for cashback. But the truth is i have done the payment through my salaried savings account debit card. So what is my fault now. This is a complete bug in their system. What am i supposed to do. This is completely unprofessional and unacceptable.