Body lab charging for members who have cancelled

My sister Kamogelo Mokgoko joined a gym the body lab whereby after few days she went back to the gym to tell them she wants to resign, they refused to give her a form to cancel her membership and now they have handed her to lawyers Bennett and associates. She only joined in September and they said the first two months are free and the monthly fee of the gym is 300 but now the lawyers letter comes and says she owes 5667 now tell me how can this amount have accumulated to that amount in six months. Body lab is a **** and they want to make quick money from so is Bennett and Associates, this person is a student and from a previous disadvantaged family and they have the audacity to send a letter for a gym that was joined in September with an amount of R5667 that is absolute madness. Body lab and Bennett and Associates are chancers big time.