Bad customer service

I had a terrible experience now with a certain accounting lady, Cecile of Family Fitness Gym in Kempton Park, I am unemployed at the moment and my son is paying for my gym contract at the moment, I therefore stopped the debitorder on my bank account, informed Cecile of my action and provided her with the EFT proof of payment of the gym fees for November 2017, she however still blocked me on the system from entering the gym and is convinced that two debitorders was reversed instead of one, I now visited my bank three times, provided her with my bankstatements for October & November 2017 to proof that only one debitorder was stopped and reversed but I still could not convince her and after many emails and personal conversations she still sticks to her story, I have no idea how to solve this and feel she is definitely giving a very good gym a very bad name due to her ignorance and bad way of dealing with the query.