Telkom holding me ransom to pay them after I had cancelled.

I cancelled my adsl contract 20 Feb 2018 on email. I am now trying to get a credit application and was informed I needed a paid up letter from Telkom. I have just got off the phone with Sifiso who confirmed they decided to only cancel 2 May 2018 and they are now advising me even though I canceled in Feb i must pay for April. This is theft in my eyes and they are doing this to numerous clients I personally know. Please can someone help me have this resolved.