Deposit Refund - COVID -19

Experienced a great Tour to Namibia so we booked again for Botswana the following year for my sister's birthday. Paid deposits for my wife, sister, and me. Then came COVID and lockdown. They requested we advance our reservation to the following year and use the same deposits. With COVID still prevailing, travelling on a Tour Bus for long periods of time at our age, did not seem to be a good idea. We requested the return of our deposits but were told "to get someone to go on our place and let them refund us our deposit". They claimed Deposits had been utilised for accommodation on Botswana, what about the Tour Buys costs?