Erroneously debited my account

In 2018 I decided to take out medical aid for my mother and younger brother who is mentally handicapped. Recently I discovered that my account is being debited with Gap cover that I never consented to. Optivest advised that as my instruction was unclear they will not refund me. This makes no sense as his medical aid I had to complete a form for them to debit my account, how do they *******ly give instruction to debit my account with no forms for a totally different cover?