MTN debited my account

Good day I bought a laptop online on the 3rd May 2021,I received a laptop.i realised that other keys on the laptop were not working.i returned a laptop on the 06th May at the Glen Mall MTN Store.After that I received a message that my contract has been cancelled.i was surprised to see that my account was debited for the laptop that I returned.i called customer service but I was not helped.On the 01st July 2021 MTN debited R5600 on my account.i called the customer service but I was not helped.