Pay up letter

I would like to log in a complaint about my account at sportcene in mpumalanga secunda where I paid up the account in 12 April 2019 but still having difficulties receiving the pay up letter as there was additional fee the store made me pay even after I have settled the account in the process of keeping me waiting for pay up latter, as the additional transaction was made on the 10th of September 2019 on the 12th September 2019 they still charged me of the same amount.It appeared today when I went to the store for follow up. When I call the lady that goes by the name of Phumela whom the account was handed over, she doesn't pick up the phone.please help me in this regard.