I'm a new member and account is over due

I'm a new member at virgin active. they contacted me to join. When I went the same day to sign up they told me its a spesial R50 sign up fee only for that day , and then I only pay in august again. And he asked me how wil I pay, and I told him its better if I pay cash, so he said they need my banking details to continue to sign up, but nt gna use my banking details . That was 26 june. This morning I get a call from them to tell me my account is in arrears, today (9 july)