I want my 80% discount as promised.

I have being called by a agent, and this lady offered me a 80% discount on my standard bank card and she told me that she will call me back with my final and full amount owing. This is so unprofessional as I am going to speak directly with standard bank due to the unprofessional services that you are rendering to the public and I will go social media live, this will also be taken legally as I am the consumer and I don't know if standard bank is dealing with a proper corporate company. The supervisor even called me and told me this was a mistake as I won't know with no proof and evedience. Give me my 80% discount as you promised and I will make payment immediately