Air India Express — Refund amount not yet credited

I have booked air ticket from SIN - TRZ 27 -MAR-2021 (PNR-WAJQPW), Due to pandamic situation flight has been cancelled, so Airindia express given the voucher against this PNR WAJQPW.

Now i check with customer care service, they said that voucher has been cancelled and refund provided to my account back (301 sgd). But untill now i have not credited any amount in my account from airindia express.

Even i have send too many mails, no reply also...