CAPTURE INCORRECT BANKING DETAILS

I joined GYM COMPANY in March and I was very excited to start my fitness journey, that didn't last long. Turns out they had captured my banking details in correctly and only informed me in June. I sent them the correct banking details and still they made no means to correct and bill the account. September I get another call from them informing me my account is in areas by some R1000+ and I must come to the gym to settle. The accounts lady was meant to call me to resolve the matter but it this day I have not received the call. I have been following with one of their employees who has been no help at all. Today I asked why they are not able to bill my account to settle the amount outstanding since they have my banking and again I am told to come to the branch, WHY? This matter can be resolved so easily without driving to either branch to deal with unhelpful employees. What do I do?