Myntra.com — not providing soft copy of invoice

Address: 400080

I purchased boat headphone from myntra.com on 22dec. Headphone stopped working after 4 months, for warranty claim, i called customer care around 20 to 30 times but each time they played bluff by saying we have sent an invoice to your mail-id but non of time i got. As per my understanding myntra sells old products on their platform because of that for warranty claim products they are not sharing the invoice to customers.