Andgo zero communication

We booked a trip to Zanzibar in 2019 paid in February 2020 for travel May 2020, Covid hit they offered a voucher for when the travel ban lifted,(fully understood this) We heard nothing from them right trough the pandemic and we had to start every line of communication, right up to re booking. We re booked for May 2021 now the package was including a flight from Mango that is now going belly up. We get nothing from them and only when i emailed the hotel and copied them in did they start communicating. now they want to "wait and see" what happens to mango and refuse to refund.