Telkom Billing Complaint.

I had a 2 year contract with Telkom, I finished paying on March 2021. I went to my nearest shop in Benoni Lakeside mall to cancel the devices and data, apparently they where allocating data every month from march till today without my knowledge. I'm disputing that because they said I'm owing R2600 which in my case doesn't make sense, I never used the data since I was unaware of the situation. It was brought to my attention recently when I wanted to upgrade, I went to different shop and even called the billing center several time and they all said there's nothing that they can do. They took me tower to post with no help. Telkom shop was a deadend so please help me.