Assumption to take a new contract without consent

I had taken out a contract for a tablet in aug 2015 from Cell U city in tygervalley, with vodacom as service provider, a 2 year contract. in Aug 2017 i knew it was coming to an end as i received an sms to confirm this. I then sent an email to cell U city in Aug 2017 to let the contract expire. After this , vodacom collected an amount (lesser than my contract amount) i then follow up in sept with cell U City, they then gave me and email address for vodacom as they said i had to cancel with them directly as its a vodacom prescription but the tablet contract was done. I then sent request to cancel to provided email address. No response end sept again, i then stopped the debit order with my bank, no further confirmation was received etc. In Jan/Feb 2018 a lady called me saying i am in arrears i explained to her that i had cancelled this and did not wish to proceed, you cannot assume that a customer wants to proceed with you after their contract expired. She asked me to send her the email i sent, i had done so, till this day no response, only sms's saying i am behind. this is unacceptable where did you ever get my consent to proceed with a contract after my original contract had expired?????????