Why am I paying for service I did not get . A service that I clearly stated that I don't

Gym Company sales representatives in Durban, Mega City have showed very big desperation. They took my information without any explainations. I had told the representative clearly that I don't want to sign up for the gym . They took my information forcibly and I've recently discovered that I them large amount of money yet I've never been to it. When I went to cancel my membership they said I was about to get blacklisted and I should atleast pay an amount of R300 . I was not even provided with an access card. Why am I paying for service I did not get ?