Byjus - Refund not received even after cancelling within the stipulated period

I was contacted by a Byju's sales representative for the UPSC exam preparation course. This was on March *, ****. The person sat with me in a *-hour video call and convinced me why Byju's was a good option for preparing for UPSC. I paid **,*** as initial instalment to join the "Super **" batch seats. I received the tablet on March **; however, books were also promised in the study materials and I had not received the books.
I complained about this to the representative who was in touch with me. He said I will receive the books once I verified the loan (I was receiving far too many calls from Byju's, some of them absolutely useless and a waste of my time, so I had blocked some numbers). I had my phone beside me every day after that to look for calls for verification from Byju's, but no such calls were received. I eventually opted to cancel the course on March **, but so far, I have not received my refund. I keep contacting their customer service number (**********) but all I receive are vacant promises of a Senior Manager contacting me within ** hours, which never happens. I'm tired of this company wasting my time and I want my money back.