Mango Airlines robbing people their hard earned money

My 3 friends and I have booked a flight for the cruise which was supposed to be a in April 2020, due to the Covid pandemic it was postponed to January. Now that the Covid cases are high and we are back to level 3, our cruise was canceled. I wrote to Mango for the refund, they told me that their tickets were not refundable. They sent me vouchers which are for 24 months. What am I supposed to do with that in this situation because covid cases are getting worse. This is day light ******* for our hard earned money.