Complaint about cellc

Good day, I cancelled my cellc contract in March, which is a month before it ended and my money was debited from my account end of May, after the month that it was suppose to be the last month, i then reversed it, I then received a statement that I'm suppose to pay double the amount end of June, when I called cellc the consultant told me that the person who cancelled my contract made a mistake and wrote that it should be cancelled in 2024,however Im suppose to pay the amount because cellc sent me their monthly benefits and I used them, but I didn't ask them to, and I cancelled the contract because I knew my financial status, I can't be responsible for the mistake that was made by one of their employees