Unauthorised charge for Jet Club

I recently made a purchase at the Jet Stores and was informed by a sales assistant that I qualify for a discount. The sales assistant did not inform me that obtaining these discounts would require me to join a Jet Club. However, when he asked that I sign a document, I noted on the document that I was asked to join the club, to which I said no. I did not take any discount and was assured that I was not part of the club. When I received my statement, I noted that I was charged for this club that I DID NOT join.

Firstly I am disappointed with the staff at Jet. To tell me that I qualify for discounts but not to mention that I need to join the Club for the discounts is *********. Had I not read the document, I would have not known. Secondly, how is it possible for me to have join this club if I said no and did not sign anything?

I want to be assured that I will not be charged further for this club and that I will be reimbursed for what was charged.