BA Unwilling to Refund Cancelled Flight

In 2020 our family had a trip planned from Johannesburg to London. Due to COVID these flight were cancelled and I requested a refund. BA refused and rather allocated vouchers. We still cannot make a trip as South Africa has been marked as a high-risk country for the UK. This rendering our vouchers useless. Trying to speak to someone at BA is useless as I'm told the only people that can help me now works from home and does not have direct contact details.