Flipkart - Wrong Name on invoice

I had ordered a redmi * phone from flipkart but after sometime i changed the owner name and flipkart sent me a confirmation message that your name has been changed. But when i recieved the phone the invoice with previous name was mentioned in that. I registered a complain for that they assured me you dont need to replace the phone we will provide you with the invoice which was mentioned in the updated name and address and ask for the time after the return period is over now they are saying once the invoice is generated it can not be changed they should have told this thing at first i registered the complain so i could have replaced the phone and ask for the new set with the name i wanted. But they consumed my return period and after that they left me with no choice now i feel cheated from flipkart.
Product details are mentioned below.
Redmi * onyx black ** gb
Order ID:
OD******************
Purchasing date: **th july ****
Delivert date: **st july.
First date of complain: **st july ****