How to remove purchaseorder from orderrepository when payment fails?

I have a thiry party payment gateway. When payment fails, i delete order reference from orderrepository. But purchnase order is still there in orderrepository. How to remove purchaseorder from orderrepository? My code is as shown below. purchnase order is showing line items.

if (paymentResponse.ResultCode != PaymentsResponse.ResultCodeEnum.Authorised)
{
_orderRepository.Delete(orderReference);
}
var purchaseOrders = _orderRepository.Load<IPurchaseOrder>(_customerContext.CurrentContactId)
                                             .OrderByDescending(x => x.Created)
                                             .ToList();