Punjab National Bank [PNB] — Refund initiated from Amazon But have not Received In Bank Account

I have ordered A Seagate Expansion 3 TB Hard Disk On 15th Of June. My Order Id is[protected]. Order Total Paid Was 5999. i Have Returned The Product & Amazon Also Initiated The Refund on 22nd of June And Gave Me A Refund reference No :- 75503721174048964758118 on 28th Of June Via Mail. 5 business Days Already Have Passed. Yet I Haven't Recived The Refund Amount In My Account. I Have Also Tried To Contact The PNB Customer Care Several Times But They Are Simply Avoiding The Whole Things By Saying That They Can't Track The Refund Reference Number. Please help me Getting My Refund.