OnePlus India — Delay in processing refund for order cancellation

I had ordered one plus via one plus website in exchange of my old phone.. but my old phone was rejected and my ordered phone was taken back and order cancelled .. now even after 13 days I have not got the refund for my order . After talking several times to customer care.. they are saying it will some more days.. refund is initiated as said by them but still not credited to my account.. Really bad service and pissed off with the delay in refund they are doing.. compared to other apps they are very very slow.