Promises go up in smoke

My late husband bought sabzenzele shares in 2010 ,the shares were to be exchanged for SAB shares in April 2020.in 2014 he passed away.In 2016 Sab was bought by ab-in-bev and so much was promised to sabzenzele shareholders for April 2020.came April 2020 none of the promises were kept and we were paid part of the money calculated by SAB and they retained 22.4%.I have been pleading with them to release the part they withheld to pay school fees and buy food they have refused.