Market trader breach contract and ********** need to cancel the contract

i want to cancel the contract i have with this company as the presentation that was given to me was false there were promises that were made that were not adhered to. i am stuck with a software that costs R20 000 and i have not even made money from it. their adminitration is poor and unfreindly. and the turtors are always busy even have back to back emails where i requested that they cancel but i am told they will not cancel, how am i supposed to continue for the product that is not doing what it is supposed to do and the presention was all a lie, please help me as i cannot continue my life like this, this has made my kids to suffer i just lost my husband and cannot deal with these people