Outsurance asks for bank details when quoting

I bought a new car and requested a an insurance quote from Outsurance because their adverts show how much every one saves with them. Their agent tried to get me to commit to the quote on the phone. I insisted on a written quote which was emailed to me. The quote was in line with all the other quotations I had received - no savings of hundreds of rands. There was no additional information on what as included or any explanation on how their cashback after 3 years works. I rep**** to the email saying I was not interested, but the email had a do not reply which meant that the agent phoned to continue the hard sell. The thing that annoyed me the most was that the agent ASKED FOR MY BANK ACCOUNT DETAILS AT THE QUOTE STAGE. How is this allowed?