Pushy for bank account details

I entered my details, find out about your, free course. I am then promoted to enter my personal banking details. I did not want to enter my account details . I shortly get a call from someone asking what problem I have giving my account details. Found quite rude . He could have phased it better. Further I don't like giving my bank details to someone pushy for my bank details for a R400 per month subscription. Having had bad experience of cancelling a credit card because of subscription I did not want. I won't give my bank details.