Jimmy offers to sell Thabo a piece of land for R50 000. Thabo sends Jimmy a letter offering to pay him R50 000 for the piece of land. But when Thabo next sees Jimmy he finds out that Jimmy has sold the land to someone else for R55 000. Thabo is upset with Jimmy and says he broke the contract between them.
Thabo sent an offer to Jimmy to buy his land but Jimmy has not accepted his offer. A contract for the sale of land must be in writing.
(See: Requirements for a contract)
Until there is a written offer and a written acceptance of that offer, there is no contract.
In this case there was no legally binding contract between Jimimy and Thabo.
There is nothing that Thabo can do to force Jimmy to sell him the land.