Agent took advantage of student

One of Virgin Actives agents came to my campus and asked me if I was interested in signing up for a membership, he wouldn't take no for an answer, so I have him my details and told him that I don't want to activate the membership just yet I still need time to think about it as I am a student and I need to budget accordingly. I received an sms from virgin active a few days later to say my account will be debited and when I gave the agent a call, to cancel the subscription that I didn't give permission to activate yet, the agent berated me asking "you signed up for the membership, why are you lying to people saying you don't want it" I then just told him to cancel it and he said he would. I woke up to a notification of a failed debit order from Virgin active today and the price it tried to debit from my account was way more than he had initially said it would be. I need to emphasis that I am a student and I need this subscription that I didn't agree to just yet to be canceled