Mango charging fees to change flights due to lockdown!

I booked a flight for me and my wife in February this year before we got locked down. The flight was supposed to be departing on the 1st of August from Cape Town to OR Thambo, but we are not allowed to travel for leisure. The contact center now told me that I may not get a voucher, because this flight is not part of their voucher trips. Now I must change my booking to a later date and it will cost me R290 per person!!! This is not my fault that we are on lockdown and now I must pay for this to be changed!! I want to e able to change my flight to December without any costs!!! This is not fair!!!