debited without signing a mandate

i am absolutely appalled right now, on the 26th of September I made an inquiry on the FNB app for medical aid, and I later received a call from Oneplan I sat through a 44-minute call. i told the consultant multiple times that I do not want the plan activated as I was still looking around at different plans, I was made to believe that the plan would not be activated. i asked for everything in writing first so I can compare the plans I was looking at, and he told me I would receive the documents via email. he told me that I would get a DebiCheck that I would have to approve before the plan was activated and that if I didn't approve it I would not be debited, I received an email on the 27th of September saying that I must accept the DebiCheck, I did not receive notification on my banking app and I did not approve anything, and because the consultant told me that the plan would not activate I just left it as I decided that oneplan would not work for me at all. today on the 1st of November my bank account was debited, and as fnb is not my main bank account this debit order has bounced, I have had perfect credit for 2 years I have never missed a debit, now this reflects badly on my credit. i phoned oneplans help line, only to be told that firstly I could not speak to a manager but also that apparently since they had my bank details that the debicheck did not even matter, they will debit my account regardless of if I had accepted it or not, and while explaining more of what happened on the original call I had, this consultant hung up the phone mid way through me explaining. this is completely unacceptable, if this matter is not resolved swiftly I will be taking this to my lawyer.