a threatening letter from gym company months later

I met a guy in joburg some time last year from gym company his name is lucky this guy asked me if id like to join the gym I told him Im not working he asked me if I have a bank account I said yes he said ok he den asked for my personal details I gave it to him fairly I kept asking him how can I join whilst I don't have money he said wen u do have it and and wen u start going to gym we will then take money from your bank account he even bought me with their printed t.shirt now I received a letter threatening me that im going to be blacklisted if I don't pay 8,299.00 where will I get that kind of money while im still looking for jobs in fact I have never been to their gym funny thing I don't even know what inside looks like, I may not know law enough but this doesn't look good on my name expecially now im a job hunter