Obstruction when trying to cancel a data only contract

I have a data only contract that I got about 5 years ago. I wanted to upgrade it to voice and data. Went to Cresta branch with all my ID docs and utility bill etc. The staff were rude and unhelpful. I was given 1 option of a plan. Not suitable so I asked that the contract be cancelled. Told that I must do it myself, they would not help. Given a number to call. Phoned it twice. After holding for a long time the agents would pick up and then hang up the phone. I could hear the chatter in the background. They simply hung up on me. Twice. I tried the messenger system of FB. I got a message to say that I needed to give them the exact date of the contract start before they would cancel. This should be on their system. I was told I must Sms CTD to 31050 and screen capture the contract date. This gave me my PHONe contract date!!! My DATA ONLY contract that I use for my tablet does not allow me to SMS!! They then wanted my ID, bank Account details etc. I forwarded these. Nothing I have spent my day trying to cancel this contract. I have physically gone into the store, phoned the supposed customer line, attempted to do on the app ( won’t allow me to) and messaged them. Still no joy. My phone is due for an upgrade and we were just about to sign up for their fibre deal. Not going to happen. What disgusting service. I only assume that they are dragging their heels as next months contract payment goes through on the 7th.