I am being harassed for something i didn't even use.

Hi, In March this year there were Virgin Active recruiters at school, after hearing them explain what they do i openned an account and i was told that as long as I am not using the card i do not have to pay. months later they started calling me saying i have to pay. then MBD INC came in, they are calling me everyday even on Sundays telling me to pay so that my Account will be fully closed and i told them I'm unemployed and I'm still a Student. my only fear is that they will blacklist me and NSFAS will not pay for my studies anymore. please help me before they blacklist me.