Poor Service and Cancellation of Contract

I am very angry and frustrated with the poor service I received from SADV VUMA FIBRE.. I have been asking them to cancel my debit order as I'm not working and till today it has not been done.. One cannot reach them as they don't provide telephonic support and the only channel you can get hold of them is through WhatsApp and email which are not helpful.. I would like to cancel my contract with them with immediate effect so that I can get another service provider as I use the internet for my child's school work.

Your urgent response will be highly appreciated.