Lufthansa Airlines — Ticket refund not received

Myself writing this complain on behalf of my sister ms. Dipannita ghosh. She had a booking with lufthansa airlines under pnr : snscob but just few days before the date of journey, lufthansa informed that one of the flights from delhi to munich has been cancelled due operational reasons. Thus i had to cancel the whole ticket. On 8th april 2020 i had cancelled the ticket over phone through lufthansa customer care executive who categorically had informed me that within the next 90days i would receive the whole amount. On 13th april i received the email confirmation of the cancelled ticket from lufthansa where i was informed that within the next 90days my refund would be credited into my credit card account. Today is the 133rd day but i haven't received my refund. What is the problem in refunding the amount i don't know. Kindly help us.