GST APPLICABLE OR NOT PAID TO MARKETING ORDER

I AM REGISTER DEALER IN GST. I AM  DISTRIBUTOR OF CELL MANUFACTURER COMPANY. ON BEHALF OF COMPANY TWO PERSONS COME FOR TAKE ORDER.

I PAY THE AMOUNT IN CASH RS. 21240. I GAVE A RETAIL INVOICE OF AMOUNT RS. 21240= 18000+1620( CGST)+1620(SGST) AS PER COMPANY RULES. THIS AMOUNT IS ADD IN MY TAXABLE VALUE . AFTER THAT COMPANY SEND ME STOCK ON ABOVE AMOUNT. I AM DOING WRONG OR RIGHT?

MY QUESTION IS THAT WHAT IS TREATMENT AS PER GST AND IN MY BOOKS OF ACCOUNT LIKE ENTRY.

INVOICE COPY IS ATTACHED.