If you cannot split the order in 2 parts, my proposal is the following :
- You make a credit note to RBTH and simultaneously an invoice to RBTY (for 30%)
- Once you receive the payment for RBTY, you reimburse RBTH.
- On our side, RBTH will send you a cancellation of the existing order and RBTY will send you the same order.
This is a bit more complicated way but this is also the cleanest way to solve the issue. For your understanding, RBTH had ordered in the name of RBTY. Indeed RBTY was not existing at that time. It is now running normally and we try to recover the situation.