Why do I need to pay for Standard Bank staff's error????

I have been with Standard Bank for more than 30 years and personally feel that I have a good credit record with them. Currently I am in the process of applying for vehicle finance and they gave me a rate of prime less 0.1%.

I was very unhappy because currently Investec gives prime less 1% and ABSA private banking also gives prime less 1%. My private banker then e-mailed me after this and told me that they are able to give me prime less 0.83% and then I agreed to that in a e-mail and accept it in writing. When I requested a copy of the agreement, my banker phoned me to tell me that she gave me the incorrect rate in the e-mail because the agreement's rate is now much higher than the one we agreed on in a e-mail.

I am currently very upset as the credit department do not want to accept the error that one of their staff made and adjust the rate to the one that I agreed on in the e-mail. This is their fault and they should man up to the error that was made, why should I now pay for an error on Standard Bank's side???

At the moment I am thinking of moving my accounts and mortgage loan to a bank that would help you with a smile and try to accommodate their customers. The reason that they do not want to change the rate as per the e-mail is because they are going to make a loss????? And then we read again in the news papers tomorrow that the directors of Standard Bank gets a huge salary but they are not able to keep their customers happy????

I am really upset and at this moment do not think much of Standard Bank and their customer service because there is none.