OnePlus - Did not processed Refund after cancelling order

I had ordered a Nord * *G device from Oneplus on **st July. I cancelled the order on *nd August due to change of promised delivery date *th to *th august. I waited for * days for refund and contacted customer service. They asked me to wait for *-* business days. After that time I contacted them again and again(**+) times. Each time they asked me to wait for *-* days and someone from their senior team will contact me, No one contacted me it till today. And they(customer support) refuse to transfer the call to the appropriate team(refund). Its been ** days from cancellation date.
This is unacceptable from a company like Oneplus.