Malindo Air - complain against Malindo Air for non refund of air fare due to cancellation of Air service

I have purchased two International flight tickets from Malindo air, to and fro from Kolkata to Kuala Lumpur , journey date **.**.**** and return journey date **.**.****. Total fare amount was charged INR **,***/-
The flight was cancelled from airline side due to covid situation.
After waiting about *.* years, when no any communication found from airline side, I initiate refund request through online. After initiating refund request , from airline side only issue a conditional travel voucher of INR **,*** (their condition is the voucher is valid only for * year for purchasing Malindo airline flights tickets and the vpucher issue only the name of passenger, if I wish to transfer the voucher to others there should be many formalities and hassles.)
Furthermore, I have paid to the Airline INR **,***/- but the airline issue a travel voucher only INR **,***/-. When I approaches to the flight company, their customer care Executive replied me by mail that INR **,***/- was the actual amount.
However, I again send my details invoice by mail and requested the flight company for refund, then they replied by mail that "please allow us time for further assistance, we will update you once we process the refund."
The journey date was **.**.****, and the flight cancellation date by the company was **.**.****, date to submitting refund request was **.**.****, but I do not get any positive assurance for refund by the flight company until now.
Also their service from Kolkata to Kuala Lumpur has been stopped still now